<PAGE>

                                                                   EXHIBIT 10.18

                          INVESTMENT ADVISOR AGREEMENT
                          ----------------------------

          This INVESTMENT ADVISOR AGREEMENT (the "Agreement") is effective as of
July 15, 2002 by and between STATE STREET BANK AND TRUST COMPANY, a trust
company organized under the laws of the Commonwealth of Massachusetts ("State
Street"), and ARIEL CAPITAL MANAGEMENT, INC. (the "Advisor").

          WHEREAS the American Bar Association Members Retirement Trust and the
American Bar Association Members Pooled Trust for Retirement Plans (collectively
referred to as the "Trusts"), for which State Street acts as trustee, are
maintained pursuant to agreements between the American Bar Retirement
Association ("ABRA") and State Street for the purpose of funding the American
Bar Association Members Retirement Plan, the American Bar Association Members
Defined Benefit Pension Plan (together, the "ABA Members Plans") and other
employee benefit plans, as adopted by eligible individuals, organizations,
partnerships, corporations or associations (each such individual employee
benefit plan being referred to as a "Plan" and collectively as the "Plans"),
which Plans must meet the requirements for qualification under Section 401 of
the Internal Revenue Code of 1986, as amended and in effect from time to time
(the "Code");

          WHEREAS, certain assets of the Trusts are deposited in a collective
investment fund, known as the MID-CAP VALUE EQUITY FUND (the "Fund"),
established under the American Bar Association Members/State Street Collective
Trust (the "ABA Members Collective Trust") established by State Street, as
trustee (the "Trustee"), pursuant to the Declaration of Trust dated December 5,
1991, as amended and in effect from time to time (the "Declaration of Trust");

          WHEREAS, the Fund is established under a group trust maintained by the
Trustee and is exempt from tax pursuant to Revenue Ruling 81-100;

          WHEREAS, the Trustee desires to retain the Advisor to act as its
investment advisor to assist the Trustee in managing such assets of the Fund as
the Trustee may designate from time to time in writing to the Advisor (the
"Subaccount") by making recommendations to the Trustee with respect to the
investment and reinvestment of the assets in the Subaccount; and

          WHEREAS the parties desire to set forth, among other things, the
duties, terms and conditions under which the Advisor will carry out such
advisory functions and the Trustee will perform certain of its functions with
respect to managing and administering the Subaccount and the Fund;

<PAGE>

                                                                               2

          NOW, THEREFORE, in consideration of the promises and mutual covenants
contained in this Agreement, it is agreed as follows:

          1. Appointment of the Advisor. The Advisor is hereby appointed and
             --------------------------
employed as investment advisor to the Trustee to assist the Trustee in its
management of such assets of the Fund as are held in the Subaccount from time to
time. The Advisor shall provide investment advice and recommendations and shall
render certain other related services to or on behalf of the Trustee, all in
accordance with the terms and conditions of this Agreement.

          2. Acceptance by the Advisor. The Advisor hereby accepts such
             -------------------------
appointment and employment and acknowledges that, (a) with respect to the assets
in the Subaccount, it is a fiduciary, as defined in the Employee Retirement
Income Security Act of 1974, as amended and in effect from time to time
("ERISA"), with respect to the Trusts and the Plans and (b) no person associated
with the Advisor is a trustee or administrator of, or an employer of anyone
covered by, any Plan. The Advisor represents that it is registered, or exempt
from registration, under the Investment Advisers Act of 1940, as amended (the
"Advisers Act"), and that it is in the business of acting as a fiduciary with
respect to assets of various retirement plans and trusts. The Advisor agrees and
covenants that it will notify the Trustee within ten (10) business days of (v)
any change of its status under the Advisers Act, (w) the receipt of formal
notice of the commencement of any proceeding by any governmental agency to take
any action which would change its status under the Advisers Act, (x) notice by
any governmental agency of the intent to place material limitations on the
activities of the Advisor, (y) notice by any governmental agency that it intends
to begin an investigation of the Advisor that is outside of the scope of routine
investigations that such agency conducts from time to time of businesses engaged
in the same or similar activities as the Advisor, or (z) notice by any
governmental agency that it has identified an area of non-compliance or other
concern in the course of any investigation of the Advisor. Throughout this
Agreement, the term "business day" shall mean any day in which the New York
Stock Exchange is open for trading and on which the Trustee's principal office
is open for business.

          3. Definition of Subaccount. The Subaccount for which the Advisor has
             ------------------------
been appointed to render investment advice and certain other services is
designated as Subaccount A and consists of the assets set forth in Appendix A.
The Trustee may change the composition of or the amount of assets included
within the Subaccount, by amending Appendix A, after written notice to the
Advisor and ABRA.

          4. The Advisor's Services.
             ----------------------

               (a) Investment Process. The Advisor shall make timely
                   ------------------
recommendations to the Trustee as to how the Trustee should invest and reinvest
the assets of the Subaccount and, in that connection, may recommend that the
Trustee purchase, sell or otherwise invest the assets of the Subaccount on the
terms and conditions recommended by the Advisor in a manner consistent with the
provisions of this Agreement. The manner and procedures for effecting any such
purchases, sales or

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                                                                               3

investments are set forth in Subsection 4(c) below. From time to time at the
request of the Trustee, the Advisor shall consult with the Trustee on a timely
basis with respect to any recommendation made by the Advisor or otherwise with
respect to the investment of the assets of the Subaccount.

               (b) Compliance With Policies and Other Requirements. In providing
                   -----------------------------------------------
its investment advice and other related services, the Advisor shall act in
accordance with the investment objectives and policies for the Fund as set forth
in the Fund Declaration pursuant to which the Fund is established and
maintained, as the same may be amended from time to time by the Trustee (the
"Fund Declaration"), a copy of which is attached hereto as Appendix B, and in
accordance with any additional investment objectives and policies that have been
established by the Trustee for the Subaccount as set forth in Appendix C, as the
same may be amended from time to time by the Trustee. In providing its
investment advice and other related services under this Agreement, the Advisor
shall comply with all of the Trustee's reasonable operating requirements as the
same may be communicated in writing by the Trustee to the Advisor from time to
time. The Advisor shall comply with any changes to such operating requirements
that the Trustee may make from time to time within a period of time reasonably
specified by the Trustee (or if none is specified, within a reasonable time
period) after notice of such changes is communicated in writing by the Trustee
to the Advisor.

               (c) Recommendation Procedures. The Advisor shall place orders or
                   -------------------------
otherwise give instructions with respect to the investment of the assets in the
Subaccount only after prior notification to and approval by the Trustee in
accordance with the provisions of this Subsection 4(c). Except in accordance
with the following provisions, the Advisor shall have no authority to place
orders for the execution of transactions involving assets of the Subaccount or
to give instructions to the Trustee with respect thereto:

                    (i) Broker List. On or prior to the first business day of
                        -----------
     each month, the Trustee shall consider brokers recommended by the Advisor
     and shall approve, to the extent deemed appropriate by the Trustee, a list
     of not more than one hundred (100) brokers through whom transactions with
     respect to the assets in the Subaccount may be effected during the
     following month (the "Broker List"). From time to time by means of Valid
     Notice (as defined below), the Advisor may request an amendment (the
     "Advisor's Amendment") to the Broker List. The Trustee shall exercise
     reasonable efforts to notify the Advisor whether or not the Trustee
     authorizes the Advisor's Amendment to the Broker List by means of Valid
     Notice within one (1) complete business day (i.e., not later than the same
                                                  ----
     time of day on the next business day) following its receipt of the
     Advisor's Amendment and if the Trustee does not so notify the Advisor, then
     the Advisor's Amendment shall be deemed to be approved at the conclusion of
     such one business day period. The Trustee may effect an amendment to the
     Broker List at any time upon Valid Notice to the Advisor.

<PAGE>

                                                                               4

                    (ii) Real-Time Recommendations. From time to time by means
                         -------------------------
     of Valid Notice (as defined below), the Advisor may make recommendations as
     to proposed transactions with respect to the assets of the Subaccount (the
     "Advisor's Recommendation"). The Advisor's Recommendation shall (A) be
     directed to the employee or employees of the Trustee designated for such
     purpose by the Trustee from time to time by Valid Notice and (B) describe
     the transaction being recommended by the Advisor in such detail and
     specificity as the Trustee may reasonably require. For this purpose, if the
     transaction is to be effected at the market price on the applicable
     exchange or trading system, a statement to such effect shall be sufficient
     to describe the proposed sale or purchase price. The Trustee shall exercise
     reasonable efforts to notify the Advisor by means of Valid Notice whether
     or not the Trustee authorizes the transaction recommended in the Advisor's
     Recommendation (the "Trustee's Response"). The Trustee shall exercise
     reasonable efforts to deliver the Trustee's Response within one (1) hour
     following its receipt of the Advisor's Recommendation and if the Trustee
     does not deliver the Trustee's Response to the Advisor within such one-hour
     period, then the transaction or transactions recommended in the Advisor's
     Recommendation shall be deemed to be approved; provided, however, that if
                                                    --------  -------
     the Advisor's Recommendation is received by the Trustee after 9:00 p.m.
     Eastern time on any business day, then the one-hour period described in
     this Subsection 4(c)(ii) shall be extended so that it expires at 9:00 a.m.
     Eastern time on the next succeeding business day.

                    (iii) Authorized Transactions. A transaction shall become an
                          -----------------------
     "Authorized Transaction" when it is (A) approved pursuant to the Trustee's
     Response or (B) deemed approved pursuant to Section 4(c)(ii). The
     designation of a transaction as an Authorized Transaction hereunder shall
     be binding against the Trustee and the Authorized Transaction shall remain
     validly approved and authorized until the earlier of (AA) the time that it
     is expressly countermanded by Valid Notice from the Trustee to the Advisor
     or (BB) at the end of the twentieth (20th) business day following its
     designation as an Authorized Transaction.

                    (iv) Investment Authority. With respect to any Authorized
                         --------------------
     Transaction, the Advisor may take any and all action necessary or desirable
     to effect such Authorized Transaction, including but not limited to (A)
     placing an order with a broker named in the Broker List for the execution
     of the Authorized Transaction and (B) issuing to the Trustee such
     instructions as may be appropriate in connection with the settlement of
     such Authorized Transaction.

                    (v) Valid Notice. "Valid Notice" shall mean (A) written
                        ------------
     notice or communication, which may be made by facsimile or by electronic
     transmission in a format and method reasonably acceptable to the Trustee,
     or (B) oral notice or communication that is recorded by the Trustee or the
     Advisor and is available for subsequent verification.

<PAGE>

                                                                               5

               (d) Custody of Assets and Confirmation of Transactions. To the
                   --------------------------------------------------
extent required by applicable law, the Advisor shall direct that all securities
purchased and the proceeds from the sale of securities for the Subaccount be
delivered to the Trustee, unless otherwise directed by the Trustee. The Advisor
shall direct any broker effecting a transaction with respect to the assets of
the Subaccount to send the Trustee a duplicate copy of any confirmation of any
such transaction, except that the Advisor may make other arrangements (which are
reasonably satisfactory to the Trustee) for the Trustee to receive such
duplicate confirmations or comparable information acceptable to the Trustee.

               (e) Communications Regarding Investment Securities. The Trustee
                   ----------------------------------------------
shall send, or cause to be sent, on a timely basis, copies of all communications
(including but not limited to proxy statements, tender offers and class action
communications) from or relating to companies, the securities or other
instruments of which are held in the Subaccount, to the Advisor. The Advisor
shall be responsible for making a recommendation to the Trustee, in such detail
and specificity as the Trustee may reasonably require, as to the appropriate
response to such communications (the "Suggested Response"). Such Suggested
Response shall be made by the Advisor by Valid Notice, at least one (1) complete
business day (i.e., not later than the same time of day or the next business
day) prior to the deadline for such response. Such Suggested Response shall be
directed to the employee or employees of the Trustee designated for such purpose
by the Trustee from time to time by Valid Notice. If the Trustee decides not to
follow the Suggested Response, it shall so notify the Advisor by Valid Notice
(the "Trustee's Rejection") not later than the earlier of one (1) complete
business day (i.e., not later than the same time of day or the next business
day) following its receipt of the Suggested Response or two (2) hours before the
response deadline. Failure by the Trustee to give the Trustee's Rejection to the
Advisor within such period shall constitute the Trustee's approval of the
Suggested Response, and shall constitute authorization to the Advisor to (i)
take such action as is appropriate to effect the Suggested Response and (ii)
issue to the Trustee such instructions as may be appropriate in connection with
effecting the Suggested Response.

               (f) Advisor's Duty of Care. The Advisor shall discharge its
                   ----------------------
duties with respect to the Subaccount solely in the interests of the
participants in the Plans and their beneficiaries with the care, skill, prudence
and diligence under the circumstances then prevailing that a prudent person
acting in like capacity and familiar with such matters would use in the conduct
of an enterprise of like character and with like aims. The Advisor shall not be
responsible for the operation or administration of the Trusts or the Plans. The
Advisor shall have no investment advisory responsibilities other than those
expressly provided in this Agreement. The Advisor shall discharge its duties in
accordance with the requirements of ERISA, other applicable law and this
Agreement.

               (g) Fidelity Bond and Insurance. The Advisor shall maintain for
                   ---------------------------
the period of the Agreement a fidelity bond meeting the requirements of Section
412 of ERISA (unless the Trustee acknowledges that the Advisor is exempt from
such requirements) and including its officers, directors and employees to the
extent so required. The Advisor will provide to ABRA and the Trustee within
twenty (20)

<PAGE>

                                                                               6

business days of the effective date of this Agreement copies of all insurance
policies (including fiduciary, errors and omissions, and fidelity bonds) that
could cover or relate to the Subaccount, the Fund, the Trusts or the Plans, and,
upon request by the Trustee or ABRA, a certificate of coverage with respect to
any such policies. The Advisor will notify ABRA and the Trustee of any material
changes in such policies, which change affects the coverage of the Advisor,
within twenty (20) business days after the earlier of when such changes are made
or are effective.

               (h) Brokerage Practices. In placing orders for the purchase and
                   -------------------
sale of assets of the Subaccount in accordance with Subsection 4(c), the Advisor
shall act in accordance with the procedures with regard to brokerage practices
for the Subaccount, as described in Appendix D. The Advisor shall make its
recommendations of brokers or dealers in accordance with its best judgment and
in a manner consistent with ERISA and other applicable law. The Advisor shall
recommend those brokers or dealers for inclusion on the Broker List using its
best judgment to choose the broker or dealer most capable of providing the
brokerage services necessary to obtain the "best available price and most
favorable execution." The Trustee recognizes that the Advisor may, in accordance
with Section 28(e) of the Securities Exchange Act of 1934, as amended, recommend
a broker or dealer who will charge a commission for effecting a securities
transaction that will exceed the amount of commission another broker or dealer
would have charged for effecting such transaction, where the Advisor has
determined in good faith that the amount of such commission was reasonable in
relation to the value of the brokerage and research services provided by such
broker or dealer to, or for the benefit of, the Subaccount, viewed in terms of
either that particular transaction or such broker or dealer's overall
responsibilities with respect to the Subaccount.

               (i) Nondisclosure of Information. To the extent necessary for the
                   ----------------------------
execution of this Agreement or to satisfy the requirements for disclosure to
participants or to meet the requirements of Sections 8 and 9, the Advisor shall
keep in strict confidence all information about the financial affairs of the
Subaccount. The Advisor may include information about the Subaccount in
aggregate information provided by the Advisor as long as the information is not
set out separately or in any other manner that would enable a third party to
determine the financial affairs of the Subaccount.

               (j) Advisor's Potential Conflicts of Interest. The Advisor (and
                   -----------------------------------------
any affiliate thereof) may engage in any other business or act as advisor to or
investment manager for any other person, even though it (or any affiliate
thereof) or such other person has, or may have, investment policies similar to
those followed by the Advisor with regard to the Subaccount. Nothing in this
Agreement shall prevent the Advisor (or any affiliate thereof) from buying or
selling, or from recommending or directing such other person to buy or sell, at
any time, securities of the same kind or class recommended by the Advisor to be
purchased or sold for the Subaccount. The Advisor shall be free from any
obligation to the Subaccount to recommend any particular investment opportunity
which comes to it. However, if the Advisor effects the purchase or sale of the
same securities for the Subaccount and other accounts at the same time that
orders are open for the Subaccount and the other accounts, the pricing of or
proceeds from such

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                                                                               7

securities shall be allocated among the other accounts and the Subaccount in a
just and equitable manner.

               (k) Valuation. At the request of the Trustee from time to time,
                   ---------
the Advisor shall provide pricing and valuation information with respect to
particular securities it has recommended for the Subaccount if the Trustee has
determined that such pricing and valuation information is not otherwise
reasonably available to the Trustee through standard pricing services.

          5. Representations by the Trustee. The Trustee represents and warrants
             ------------------------------
that (a) there are no restrictions or limitations on the Subaccount's
investments imposed by applicable law other than (i) those set forth in the
Declaration of Trust, the Fund Declaration, this Agreement, and Appendix C, as
any of the same may be amended from time to time and communicated to the
Advisor, (ii) those provided in ERISA and (iii) any other investment restriction
or limitation imposed by law or regulation which in the Trustee's judgment is
applicable to the Subaccount and which is communicated by the Trustee to the
Advisor; and (b) disclosure to Plan participants contained in the Registration
Statement describing the Subaccount is accurate and prepared in accordance with
the requirements of Form S-1 under the Securities Act of 1933, as amended,
except that the Trustee makes no representation or warranty with respect to any
disclosure relating to the Advisor or its services with respect to the
Subaccount which the Advisor has prepared, approved in writing or has not
disapproved within five (5) business days following confirmed transmission by
facsimile, acceptable electronic transmission or overnight mail to a person
designated by the Advisor to review such disclosure.

          6. Liability of the Advisor; Indemnification.
             -----------------------------------------

               (a) Limitation of Liability of the Advisor. The Advisor shall not
                   --------------------------------------
be liable for any act or omission of any other person or entity exercising a
fiduciary responsibility, if such fiduciary responsibility has been allocated to
such other person or entity in accordance with this Agreement, the Declaration
of Trust, the Fund Declaration, the Plans or the Trusts, except to the extent
that the Advisor has itself violated its fiduciary responsibility or its
obligations under this Agreement, or except to the extent that applicable law
(including ERISA) may expressly provide otherwise.

               (b) Indemnification.
                   ---------------

                    (i) Indemnification of Advisor. To the extent permitted by
                        --------------------------
     applicable law, the Trustee agrees to indemnify and hold harmless the
     Advisor for losses, damages or expenses resulting from (A) actions taken by
     the Advisor in reliance on information provided by the Trustee to the
     Advisor in accordance with this Agreement, including but not limited to the
     Trustee's operating requirements and cash availability information, (B)
     actions omitted to be taken by the Advisor pursuant to instructions or
     directions provided by the Trustee and/or (C) valuation of the assets held
     in the Subaccount, computation of unit values for the Subaccount by the
     Trustee, or performance data and other financial information provided by
     the Trustee to Subaccount participants except to

<PAGE>

                                                                               8

     the extent that the Advisor has incorrectly reported or failed to report
     securities transactions in the Subaccount to the Trustee as provided in
     this Agreement and to the extent that any error in such valuation or
     computation is due to prices or other information provided by the Advisor.

                    (ii) Indemnification of the Trustee. To the extent permitted
                         ------------------------------
     by applicable law, the Advisor agrees to indemnify and hold harmless the
     Trustee for any losses, damages or expenses resulting from (A) any
     recommendation of the Advisor or based on information provided by the
     Advisor, (B) the Advisor's failure to provide correct and timely
     information or to make recommendations on a timely basis as provided in the
     Agreement, and (C) any disclosure relating to the Advisor or the services
     provided by the Advisor with respect to the Subaccount which the Advisor
     has prepared, approved in writing or has not disapproved within five (5)
     business days following transmission by facsimile, acceptable electronic
     transmission or overnight mail to a person designated by the Advisor to
     review such disclosure; provided, however, that the Advisor shall not be
                             --------  -------
     required to indemnify and hold harmless the Trustee to the extent that such
     losses, damages or expenses result from an act or omission of the Advisor
     with respect to which the Advisor not only has used such care, skill,
     prudence and diligence as a reasonably prudent person acting in like
     capacity and familiar with such matters would use in the conduct of an
     enterprise of like character and with like aims, but also has otherwise
     acted in accordance with this Agreement.

                    (iii) Advisor and Trustee Indemnification Procedures. If the
                          ----------------------------------------------
     party seeking indemnification is either the Advisor or the Trustee, such
     party shall promptly notify the indemnifying party of any claim, action,
     suit or proceeding, or threat thereof, which may result in a claim for
     indemnification. Upon such notification, the indemnifying party may, at its
     option, undertake the conduct and cost of defending any such claim, action,
     suit or proceeding and in such case shall have full control of such
     defense, including but not limited to selection of counsel (provided that
     such counsel must be reasonably acceptable to the party being indemnified)
     and entry into settlement agreements (provided that any such settlement
     agreement shall require the consent of the party being indemnified, which
     consent shall not be unreasonably delayed or withheld). The Trustee or the
     Advisor, as the indemnifying party, shall not be liable for any legal or
     other expenses incurred in connection with any such defense that were not
     specifically authorized by it; provided, however, if such indemnifying
                                    --------  -------
     party fails to undertake and prosecute vigorously the defense of any such
     claim, action, suit or proceeding, it shall be liable for reasonable legal
     and other expenses incurred by the party being indemnified.

               (c) Indemnification of ABRA.
                   -----------------------

                    (i) To the extent permitted by applicable law, the Advisor
     agrees to defend, indemnify and hold harmless ABRA, its then present and
     former officers, directors and advisory directors, the ABA, and its then

<PAGE>

                                                                               9

     present and former officers and Board of Governors (the "Indemnified
     Persons") against any and all expenses (including attorney's fees,
     judgments, fines and penalties, including any civil penalties assessed
     under Section 502(l) of ERISA) and amounts paid in settlement actually or
     reasonably incurred in connection with any threatened, pending or current
     action, suit, proceeding or claim, whether civil, criminal, administrative
     or otherwise, and the amount of any adverse judgment entered against any of
     them and any reasonable expenses attendant thereto by reason of any of the
     Advisor's acts or omissions in connection with this Agreement. For the
     above defense, indemnity and hold harmless provision to apply (i) the
     Indemnified Persons (or ABRA) shall inform the Advisor promptly of any
     claims threatened or made against any Indemnified Person, (ii) the
     Indemnified Persons shall cooperate fully with the Advisor in responding to
     such threatened or actual claims and (iii) any settlement agreement entered
     into by the Indemnified Persons shall require the written approval of the
     Advisor, which approval shall not be unreasonably withheld or delayed, and
     any settlement agreement entered into by the Advisor shall require written
     approval, within the time frame established by the Advisor, of the
     Indemnified Persons, which approval shall not be unreasonably withheld.

                    (ii) Right to Counsel. The Indemnified Persons shall have
                         ----------------
     the right to employ counsel in their, its, his or her sole discretion. Such
     Indemnified Persons shall be responsible for the expenses of such separate
     counsel except as provided in Subsection 6(c)(iii). The Advisor agrees to
     cooperate fully with the Indemnified Persons and their separate counsel in
     responding to such threatened or actual claims.

                    (iii) Separate Counsel. The Advisor agrees to cooperate
                          ----------------
     fully with the Indemnified Persons in responding to such threatened or
     actual claims. The Indemnified Persons shall have the right to reasonable
     expenses of separate counsel paid by the Advisor, provided that the Advisor
                                                       --------
     shall not be liable for any legal or other expenses incurred in connection
     with any such threatened claim or defense that were not specially
     authorized by the Advisor in writing and provided that the Advisor shall
                                              --------
     have received a written opinion reasonably acceptable in form and substance
     to the Advisor of counsel reasonably acceptable to the Advisor (and which
     counsel shall not represent or otherwise be affiliated with any of the
     Indemnified Persons) that there exists a material conflict of interest
     between one or more of the Indemnified Persons and the Advisor in the
     conduct of the response to a threatened claim or in the conduct of the
     defense of an actual claim, in which event the Advisor shall be liable for
     the reasonable legal expenses of each counsel whose appointment is
     necessary to resolve such conflict; provided, however, the Advisor shall
                                         --------  -------
     not be responsible for more than one (1) counsel for all Indemnified
     Persons and selection of such counsel shall be reasonably acceptable to the
     Advisor.

                    (iv) Payment of Expenses. Expenses (including counsel fees)
                         -------------------
     specifically authorized by the Advisor and actually and reasonably incurred
     by the Indemnified Persons in defending against or responding to such
     threatened

<PAGE>

                                                                              10

     or actual claims as provided in (i) and (iii) of this Subsection shall be
     paid as they are incurred. If an Indemnified Person is reasonably required
     to bring any action to enforce rights or collect monies due under
     Subsection 6(c) and is successful in such action, the Advisor shall
     reimburse such Indemnified Person or its subrogee for reasonable fees and
     expenses incurred in bringing and pursuing such action.

                    (v) Supplemental Rights. Indemnification pursuant to
                        -------------------
     Subsection 6(c) is intended to be supplemental to any other rights to
     indemnification available to the Indemnified Persons. Nothing herein shall
     be deemed to diminish or otherwise restrict the Indemnified Persons' rights
     to indemnification under law.

                    (vi) Third Party Beneficiaries. The indemnifying party
                         -------------------------
     acknowledges that the Indemnified Persons are intended to be third-party
     beneficiaries of Subsection 6(c).

          7. Transactions Prohibited with Respect to the Advisor. The Advisor,
             ---------------------------------------------------
its officers, partners, directors and affiliates, and each of them, shall not,
with respect to the Subaccount, (a) as a principal, purchase assets from or sell
assets to the Fund, (b) receive any compensation or fees with respect to the
Fund, other than the fees provided for in Appendix E, (c) engage in or recommend
any transaction involving or affecting the Fund that such person knows or should
know is a prohibited transaction under ERISA unless such transaction is exempt
under the applicable provisions of ERISA or (d) direct delivery of securities or
payment to itself or direct any disposition of securities or cash from the
Subaccount except to the Trusts.

          8. Reports and Meetings.
             --------------------

               (a) Monthly Reports. At least monthly the Advisor shall render to
                   ---------------
the Trustee and ABRA, or their designee, reports concerning its services under
this Agreement and the status of the Subaccount, based on the reporting
procedures set forth in Appendix F, which is hereby adopted and made a part of
this Agreement, including statements of investments in the Subaccount.

               (b) Meetings. The Advisor will meet with the Trustee and ABRA and
                   --------
with such other persons as the Trustee or ABRA may designate on reasonable
notice and at reasonable times and locations, to discuss general economic
conditions, Subaccount performance, investment strategy and other matters
relating to the Subaccount.

               (c) Reports Prior to Termination. On each day during the period
                   ----------------------------
ten (10) business days prior to the effective date of the Advisor's resignation
or its removal under this Agreement by the Trustee (the "Termination Date"), or
on each day of such shorter period after which the Advisor has received notice
of its removal, the Advisor shall render to the Trustee and ABRA, or their
designee, a report of the current status of the Subaccount based on the
procedures set forth in Appendix F, including a statement of investments in the
Subaccount and on the day immediately following the

<PAGE>

                                                                              11

Termination Date, such report shall be rendered in final form with respect to
the status of the Subaccount, including a statement of investments therein, as
of the close of business on the Termination Date.

               (d) Additional Reports. The Advisor shall furnish to the Trustee
                   ------------------
and ABRA such additional reports and information as may be reasonably requested
by the Trustee or ABRA.

          9. Accounting. The Advisor shall keep accurate and detailed records
             ----------
concerning its services under this Agreement, including records of all
transactions effected and recommendations made during its performance of this
Agreement, and all such records shall be open to inspection at all reasonable
times by the Trustee and ABRA, or their designee, and by duly authorized
representatives of the Secretary of Labor and the Secretary of the Treasury
acting pursuant to their authority under ERISA and the Code, respectively, and
other appropriate regulatory authorities.

          10. Advisor's Compensation. The amount and manner of payment of fees
              ----------------------
payable by the Trustee to the Advisor for the Advisor's services under this
Agreement are set forth in Appendix E. The Advisor agrees that if it enters into
a fee schedule with any new non-eleemosynary client whose portfolio is advised
or managed under the same investment policies and objectives as the Subaccount,
and is similarly or smaller sized, for services which are similar to the
services provided under this Agreement and such fee schedule contains fees that
are less than the fees set forth in Appendix E, it will offer the same fee
schedule to the Trustee, which shall have the right to require the amendment to
Appendix E to reflect that lower fee schedule.

          11. Removal and Resignation.
              -----------------------

               (a) Removal of the Advisor. Upon written notice to the Advisor,
                   ----------------------
the Advisor may be removed by the Trustee. Any transaction for the Subaccount
authorized by the Trustee prior to the receipt by the Advisor of the notice
shall be consummated, and the Advisor shall not recommend any transaction for
the Subaccount subsequent to the receipt of the notice.

               (b) Resignation of the Advisor. The Advisor may resign under this
                   --------------------------
Agreement upon sixty (60) days' prior written notice to the Trustee. The Advisor
shall concurrently advise ABRA in writing of such resignation and the effective
date thereof.

               (c) Termination of Obligations. The respective obligations of the
                   --------------------------
Advisor and the Trustee under Section 6 of the Agreement shall survive any such
removal or resignation or other termination of this Agreement.

          12. Termination, Amendment or Modification. The provisions of this
              --------------------------------------
Agreement may not be terminated, changed, modified, altered or amended in any
respect except in a writing signed by the parties.

<PAGE>

                                                                              12

          13. Definitions. As used herein the following terms shall have the
              -----------
meanings ascribed to them in the following sections of this Agreement:

Term Defined                      Section
------------                      -------

ABA Members Collective Trust      Introduction
ABA Members Plans                 Introduction
ABRA                              Introduction
Advisers Act                      2
Advisor                           Introduction
Advisor's Amendment               4(c)(i)
Advisor's Recommendation          4(c)(ii)
Agreement                         Introduction
Authorized Transaction            4(c)(iii)
Broker List                       4(c)(i)
business day                      2
Code                              Introduction
Declaration of Trust              Introduction
ERISA                             2
Fund                              Introduction
Fund Declaration                  4(b)
Indemnified Persons               6(c)(i)
Plans                             Introduction
State Street                      Introduction
Subaccount                        Introduction
Suggested Response                4(e)
Termination Date                  8(c)
Trustee                           Introduction
Trustee's Response                4(c)(ii)
Trustee's Rejection               4(e)
Trusts                            Introduction
Valid Notice                      4(c)(v)

          14. Governing Law. This Agreement shall be construed and enforced
              -------------
according to the laws of The Commonwealth of Massachusetts and, to the extent of
any federal preemption, the laws of the United States of America.

          15. Binding upon Successors. This Agreement shall be binding upon and
              -----------------------
enforceable by the successors to the parties hereto.

          16. Assignment. The Advisor may not assign this Agreement (including
              ----------
for this purpose any assignment within the meaning of the Advisers Act), or any
rights or responsibilities hereby created, without the prior written consent of
the Trustee, which consent may be withheld by the Trustee in its sole
discretion; however, the parties may amend this Agreement from time to time in
accordance with Section 12.

<PAGE>

                                                                              13

          17. Notices. Written notices shall be deemed effective with respect to
              -------
a party upon delivery to such party at the address set forth below or to such
other address as may be provided in writing from time to time by such party:

     To the Advisor:
                       ---------------

                       ---------------

                       ---------------
                       Attention:
                       Telecopier:
                                  -------------

     To the Trustee:   State Street Bank and Trust Company
                       Batterymarch Park III
                       Three Pine Hill Drive
                       Quincy, Massachusetts 02169
                       Attention: ABRA Division Head

     If by mail to:    State Street Bank and Trust Company
                       Post Office Box 1389
                       Boston, Massachusetts 02104
                       Attention:  ABRA Division Head

          18. Oral Communications. Oral communications between the parties to
              -------------------
this Agreement shall be effective hereunder only to the extent specifically
authorized herein. By its execution of this Agreement, each of the parties
hereto acknowledges that the other party may record any such oral communications
and consents to any such recording. All oral communications shall be confirmed
in writing, except that if an oral communication is recorded such recording
shall be controlling and no written confirmation shall be required.

          19. Authority. The parties to this Agreement represent, respectively,
              ---------
that they have duly authorized the execution, delivery and performance of this
Agreement and that neither such execution and delivery nor the performance of
their obligations hereunder conflict with or violate any provision of law, rule
or regulation, or any instrument to which either is a party or to which any of
their respective properties are subject and that this Agreement is a valid and
binding obligation.

          20. Authorized Representatives of the Advisor. The Advisor from time
              -----------------------------------------
to time shall by written notice certify to the Trustee the name of the person or
persons authorized to act on behalf of the Advisor. Any person so certified
shall be deemed to be the authorized representative of the Advisor. The Advisor
shall give written notice to the Trustee when any person so certified ceases to
have the authority to act on behalf of the Advisor, but such revocation of
authority shall not be valid until the notice is received by the Trustee. The
Advisor will notify the Trustee in writing of any significant changes in the
officers of the Advisor and any changes in the personnel of the Advisor
responsible for providing investment advice with respect to the assets of the
Subaccount within twenty (20) business days after such change.

<PAGE>

                                                                              14

          IN WITNESS WHEREOF, the parties have executed this Agreement as of the
15th day of July, 2002.

                                            TRUSTEE:
                                            -------

                                            STATE STREET BANK AND TRUST
                                               COMPANY


Attest:                                     By
       ---------------------------------      ----------------------------------
       Name:                                  Name:
       Title:                                 Title


                                            ADVISOR:
                                            -------

                                            ARIEL CAPITAL MANAGEMENT, INC.


Attest:                                     By
       ---------------------------------      ----------------------------------
       Name:                                  Name:
       Title:                                 Title

<PAGE>

                                   APPENDIX A

                            Assets in the Subaccount

     The assets in Subaccount shall consist of the following assets:

     (a) All assets held in the Fund on July 15, 2002; and

     (b) All amounts subsequently contributed or transferred to the Fund; and

     (c) All interest, income and gains attributable to such amounts; minus

     (d) All losses attributable to the amounts described in clauses (a) through
(c) above; minus

     (e) All amounts withdrawn or transferred from the Fund (not including
amounts withdrawn to pay fees and expenses); minus

     (f) A pro rata portion of the fees and expenses for the Fund (except for
the fees and expenses chargeable directly for the advisory services, management,
administration, custody and accounting for the Subaccount and any other
subaccounts of the Fund); minus

     (g) The amounts withdrawn to pay the fees and expenses chargeable directly
for the advisory services, management, administration, custody and accounting
for the Subaccount.

<PAGE>

                                   APPENDIX B

                                Fund Declaration

<PAGE>

                                   APPENDIX C

                Additional Investment Objectives and Restrictions

     The Investment Advisor shall not recommend an investment:

          (i)  if such investment, at the time of purchase, would cause more
               than 5% of the assets of the Subaccount to be invested in
               warrants generally, or more than 2% of the assets of the
               Subaccount to be invested in warrants not listed on a nationally
               recognized United States securities exchange;

          (ii) if such investment, at the time of purchase, would cause more
               than 10% of the assets of the Subaccount to be invested in
               illiquid securities, including repurchase agreements with
               maturities in excess of seven days or portfolio securities that
               are not readily marketable;

          (iii) in any industry, if such investment, at the time of purchase,
               would cause more than 25% of the assets of the Subaccount to be
               invested in such industry;

          (iv) in securities of an issuer if such investment, at the time of
               purchase, would cause more than 5% of the assets of the
               Subaccount to be invested in the securities of such issuer; or

          (v)  if such investment, at the time of purchase, would cause more
               than 15% of the assets of the Subaccount to be invested in
               foreign securities, including ADRs.

<PAGE>

                                   APPENDIX D

                               Brokerage Practices

     The Investment Advisor has provided the Trustee with a copy of Part II of
the Form ADV most recently filed by the Investment Advisor with the Securities
and Exchange Commission, in which form the general brokerage practices of the
Investment Advisor are described. The Investment Advisor will from time to time
provide the Trustee with amendments to such form, in accordance with applicable
law.

<PAGE>

                                   APPENDIX E

                                  Advisor Fees

     For its services rendered as investment advisor under the Agreement, the
Investment Advisor will be compensated at the annual rates set forth below,
based on the aggregate value of the assets in the Subaccount. Such compensation
shall be calculated and accrued on a daily basis and paid monthly from the
assets of the Subaccount.

Value of Assets in Subaccount            Rate

First $20 million                        .75%

Over $20 million                         .50%

<PAGE>

                                   APPENDIX F

I.   Operational Procedures Between the Trustee and the Advisor

     A. It is understood and agreed that the Trustee:

          1.   holds title to all of the assets of the Subaccount;

          2.   is responsible to assure that investments made for the Subaccount
               meet applicable requirements and limitations;

          3.   is required to value such assets; and

          4.   will maintain the proper accounting records for the Subaccount.

     B. Cash.

          1.   The Trustee will communicate daily to the Advisor by 12:00 noon
               (Eastern Time) the cash available for investment in the
               Subaccount, which information will be based on the procedures set
               forth below.

          2.   Extraordinary cash flow requirements - In the event the Trustee
               becomes aware of facts that will require the withdrawal of an
               extraordinary amount of cash from the Subaccount under the Plans,
               the Trustee will promptly communicate to the Advisor such facts,
               including the amount and date of such cash withdrawal.

     C. The Advisor will communicate to the Trustee purchases and sales of
investments in the Subaccount as follows:

          1.   Common Stock and Long-Term Debt Securities.

          (a)  The Advisor will communicate daily to the Trustee no later than
               9:00 p.m. (Eastern Time) on the trade date all purchase and sale
               transactions for the Subaccount. Each daily report will indicate
               separately number of purchases and sales and total trades. On
               days when no trades are recommended the Advisor will issue a
               negative trade report. Such communication will include the
               following information for each trade:

               .    Buy or sell

               .    Trade date (if as of trade)

               .    Settlement date

               .    Name of broker or dealer or other party

<PAGE>

                                                                               2

               .    Name of issue

               .    CUSIP number/Cedel

               .    Number of shares (or principal amount in local currency if
                    debt security)

               .    Price per share (or principal amount if debt security) in
                    local currency

               .    Price per share (or per $100 (or local equivalent) of debt
                    security) in local currency

               .    (For debt) Interest purchased or sold

               .    Agreed upon commission per share (or per other unit of
                    interest)

               .    Total commission

               .    Exchange on which transaction is executed (or transacted
                    over the counter)

               .    Net amount

               .    Such other information as may be required by the Trustee

               .    Clearing broker ("same" if same as trading broker)

               .    SIC Code

          (b)  For DTC eligible securities and when applicable, the Trustee
               shall confirm to DTC, as soon after trade date as possible,
               through an acknowledgement procedure acceptable to DTC and the
               Trustee, all trades which accurately reflect the trades entered
               into for the Subaccount as reported to the Trustee by the
               Advisor.

          (c)  The Advisor will arrange for a copy of each confirmation to be
               sent to the Trustee or an affiliate as designated by the Trustee.

     2.   Short-Term Debt Securities

          (a)  As of 10:30 a.m. (Eastern Time) on each business day, the Trustee
               will invest available cash in the Subaccount by purchasing and
               selling units for the Subaccount in the Yield Enhanced Short Term
               Investment Fund ("YES"), unless the Advisor notified the Trustee
               prior to such time that the Advisor recommends investment in
               accordance with paragraph b. The Trustee shall confirm daily the

<PAGE>

                                                                               3

               number of units purchased and sold on the preceding day, as well
               as the YES unit value at the close of business on the preceding
               day.

          (b)  Alternatively, the Advisor may notify the Trustee in advance in
               writing that the Advisor recommends that the Trustee invest
               available cash in the Subaccount.

               (i)  In such event, the Advisor will communicate daily to the
                    Trustee or an affiliate no later than 10:00 a.m. (Eastern
                    Time) all recommended purchase and sale transactions in
                    short-term securities to be made for the Subaccount. Such
                    communication will include the following information for
                    each trade:

               .    Buy or sell

               .    Trade date (if as of trade)

               .    Settlement date

               .    CUSIP number/Cedel

               .    Name of broker or dealer or other party, if other than the
                    issuing company

               .    Name of issue

               .    Current par value in local currency

               .    Cost of acquisition or proceeds of sale

               .    Last coupon date

               .    Discount or interest rates

               .    Maturity date of purchase

               .    Collateral

               .    Currency

               .    Such other information as may be required by the Trustee

               (ii) The Advisor also will direct each executing broker or dealer
                    or other party or the issuing companies to deliver or
                    receive the securities against payment for the account of
                    the Trustee.

<PAGE>

                                                                               4

               (iii) The Trustee will convey to the Advisor no later than the
                    next business day a report showing in detail the previous
                    day's transactions based on the procedures set forth in
                    Section II below. The Advisor will (a) promptly check the
                    data in such report and (b) immediately advise the Trustee
                    by telephone (followed by a written confirmation within two
                    days) of any variances.

               (iv) If such investments are held to maturity the Trustee will
                    redeem such securities on the maturity date and make the
                    funds available to the Advisor for reinvestment.

               (v)  The Advisor will also direct each broker or dealer or party
                    or issuing company to convey a copy of each confirmation to
                    the Trustee.

II.  Valuation and Accounting of the Subaccount

     A.   The assets of the Subaccount are valued as provided in the current
          prospectus included in the registration statement filed with the
          Securities and Exchange Commission.

     B.   Stocks and long-term debt security transactions will be recorded not
          later than the business day following the trade date. Dividend income
          will be recorded on the ex-dividend date. Interest income will be
          accrued daily.

III. Communications to Investment Advisor

     A.   State Street will send the following reports on a monthly basis to the
          Advisor by overnight mail so that they are received no later than the
          tenth business day of the following month:

          .    Statement of Investments showing account holdings as of the last
               day of the month.

          .    Monthly Summary of Account Activity Report (Trials).

          .    Daily Purchase Activity Report (Purchases and Sales Report).

          .    Daily Sales Activity Report (Purchases and Sales Report).

          .    Actual Dividend Receipts Reports (Dividend and Interest Report).

          .    Summary of Accounting Journals Report - This report displays a
               daily summary of client contributions, client withdrawals and
               expenses charged to the account (Cash Summary Report).

<PAGE>

                                                                               5

          .    Stock Dividend/Stock Split Schedule Report. Mergers, spinoffs,
               exchanges, etc. will also be indicted on this report as they
               occur.

          .    YES Report. (This report will be distributed only if the
               Subaccount participates in YES for short term investments.)

     B.   State Street will send the Advisor the existing broker list within two
          business days prior to the end of each month to determine whether any
          changes will be made under Section 4(c) of the Agreement.

     C.   The Advisor will send the following reports (or information) to the
          Trustee:

          .    Monthly holdings (at month end) with security, # shares, price,
               yield, cost and market value.

          .    List of transactions (purchase and sales) for the month with
               security, # shares and per share sale total.

          .    Monthly return on portfolio, gross of fees.

IV.  Notices

     The methods of communication and the persons to whom the information
     required by this Appendix F will be given, will be set forth in writing
     between the Trustee and the Advisor from time to time as required by the
     circumstances to carry out the intent and purposes of the Agreement and
     this Appendix F.