NORTH AMERICAN UPPER CRETACEOUS CORALS OF THE: GENUS 

MICRABACIA. 

By LLOYD WILLIAM STEPHENSON. 

INTRODUCTION. 

Corals are meagerly represented in the Upper 

Cretaceous deposits of North America, and 

much of the material is in a poor state of preservation and can not be satisfactorily identified, 

either generically or specifically. It is important, therefore, to place on record descriptions 

and illustrations of some well-preserved corals 

of the genus Micrabacia from the Atlantic and 

Gulf Coastal Plain and from the western interior of the United States. The specimens 

from the Coastal Plain, with the exception of 

those from New tTersey and one lot from Mississippi, are in a much better state of preservation than those I have seen from either the 

western interior or Europe, though most of 

~hem are soft and to insure their safe handling 

It was found best to harden them with a dilute 

solution of white shellac. 

Seven specie:;;; and two varieties have been 

1·ecognized. All are new with the exception of 

Micrabaci-a americana :Meek and Hayden which . . . ' 

was originally described from poorly preserved 

specimens found in South Dakota. They are 

all repres~nted by small, free, disk-shaped, simple (that Is, not colony forming) corallites, not 

exceeding 10 millimeters in diameter. On account of their small size it is necessary to study 

the specimens under a lens of moderately high 

power, and to figure them adequately it is necessary to enlarge them four to eight times. 

One of the new species, M. cr·ibraria, occurs 

in the upper part of the Black Creek fo~mation 

in North Carolina and the lower part of the 

Ripley fon:nation in ~a.bama. Poorly preserved speCimens, questwnably referred to this 

species, have been found in the lower part of the 

S~lma chalk in Mississippi, and specimens in a 

still poorer state of preservation but apparently having the same type of b.a.sal sculpture 

occur in the Woodbury clay in New Jersey. 

The strata exposed at all these localities are of 

approximately the same age and. occur in the 

upper part of the zone of Exogyrn ponderosa, a 

fossil zone which has been traced from New 

Jersey to Mexico. So far as known, therefore, 

this species is confined within narrow stratigraphic limits and will probably prove to be a 

valuable index fossil. 

All the other Atlantic and Gulf coast species 

occur in the zone of Exogyra costata, which 

overlies the Exogyra ponderosa zone and which 

also has been traced from New Jersey to 

Mexico. Micrabacia americana 1\Ieek and Hayden and its variety multicostata are found in 

the upper part of the Montana group of the 

western interior of the United States, in beds 

that correspond in age to the zone of Exogyra 

costata. None of these forms are known to 

have a very wide geographic range, but within 

faunal subprovinces they will probably prove 

to be useful horizon indicators. 

Little is known of the race historv of the 

genus. The oldest species referred to" it is M. 

beaumontii Milne-Edwa.rds and Haime, from 

the lower· part of the Lower Cretaceous (N eocomian), Caussols, Department of V ar, France. 

If this species was correctly identified the genus therefore ranges through the Cretaceous, 

but its pre-Cretaceous ancestors are unknown, 

and apparently it became extinct before the 

beginning of the Eocene. 

The type species of the genus is M. coronula 

(Goldfuss), from the chalk of Essen, Germany. 

Milne-Edwards and Haime 1 have described one 

species, M. beaumontii, from the N eocomian of 

1 Annales sci. nat., 3d ser., vol. 15, p. ~, 1851. 

115 
116 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

Caussols, Department of Var, France; Duncan 1 

has described a species, M. fittoni, from the 

Gault (Albian) of Folkestone, England; and 

Bolsche 2 has described a species, M. senoniensis, from the Upper Senonian of Gehrden, Germany, where it is associated with Belemnitella 

mucronata Schlotheim. I have compared the 

American material with typical specimens of 

the type species, M. coronula (Goldfuss), and 

have confirmed their generic identity. Examples of M. beaumontii, M. jittoni, and M. senoniensis are not available for comparison, and 

the figures are poor, so that I have not been able 

to verify the correctness of their reference to 

Micra bacia. 

In 1905 T. Wayland Vaughan (see synonymy, 

below) made the genus the type of the new family Micrabaciidre, under which he also included 

the genera Diafungia Duncan, Microsmillia 

Koby, Podoseris Duncan, and Antilloseris 

Vaughan. This paper has been prepared under 

the supervision of Mr. V.aughan, to whom I am 

inJebted for references to literature and for 

constructive criticism in regard to the generic 

relations, the classificatory value of the coral 

characters, and the use of terms. 

Mr. T. W. Stanton has informed me of the 

stratigraphic position of the specimens from 

the western interior, most of which were inadequately labeled. 

The specimens of Micrabacia from Maryland 

were collected by Messrs. Stanley Worden and 

M. I. Goldman; those from North Carolina, by 

me; those from the Chattahoochee region and 

Alabama, by Mr. Stanton and me; those from 

Mississippi, by me; those from Texas, by Mr. 

R. H. Bruce;· and those from the western interior by Messrs. Stanton, F. H. Knowlton, 

Homer Squyer, H. M. Robinson, V. H. Barnett, C. J. Hares, C. E. Siebenthal, and W. C. 

Knight. 

1 British fossil corals, 2d ser., pt. 2, p. 37, pl. 14, figs. 6-9: Paleontographical Society, vol. 23, 1870. 

2 Deutsch. geol. Gesell. Zeitschr. ,Band 18, pp. 472, 473, pl. 9, fig. 1, 1866. 

SYSTEMATIC DESCRIPTIONS. 

Genus MICRABACIA Milne-Edwards and Haime. 

1816. Cyclolites. William Smith (not Lamarck), Strata 

identified by organic fossils, p. 15. 

1826. Fungia. Goldfuss, Petrefacta Germanire, vol. 1, p. 

50, pl. 14, fig. 10. 

1840. Fungia. F. A. Roemer(notLamarck), DieVersteinerungen des norddeutschen Kreidegebirges, p. 25. 

1849. Micrabacia. Milne-Edwards and Haime, Compt. 

Rend. Paris Acad. Sci., vol. 29, p. 71. 

1850. Micrabacia. Milne-Edwards and Haime, A monograph of the British fossil corals, p. xlvii, Paleontographical Society. 

1851. Micrabacia. Milne-Edwards and Haime, Annales 

sci. nat., 3d ser., Zoologie, vol. 15, p. 88. 

1860. Micrabacia. Milne-Edwards, Histoire naturelle des 

coralliaires, vol. 3, p. 29 (amended). 

1869. Micrabacia. Duncan, A monograph of the British 

fossil corals, 2d ser., pt. 2, p. 24, Paleontographical 

Society, vol. 22. 

187G. Micrabacia. Meek and Hayden, A report on the 

invertebrate Cretaceous and Tertiary fossils of the 

upper Mie3ouri country: U. S. Geol. and Geog. 

Survey Terr. Rept., vol. 9, p. 1. 

1884. Micrabacia. Duncan, Linnean Soc. London Jour., 

Zoology, vol. 18, p. 143. 

1905. Micrabacia. Vaughan, U. S. Nat. Mus. Proc., vol. 

28, p. 387. 

Type species, Fungia coronula Goldfuss. 

The most complete previous description of 

the genus is that given by Duncan: 

Corallum simple, free, lenticular, broader than high, 

convex above, slightly concave at the base, which has a 

circular outline. Calice with a small shallow axial depression, filled by a false columella, from which the principal 

septa radiate, being joined with those of the higher orders 

toward the circumference. Septa numerous, solid, imper• 

forate, arched above, with a perpendicular outer edge. 

Costre distinct on the base, bifurcating at the edge, a 

process from two costre forming a septum. Intercostal 

spaces continuous with the line of direction of the septa, 

crossed by synapticula in concentric rows, and perforate 

between the synapticula. Interseptal loculi crossed by 

large and small synapticula, which radiate from the base 

in discontinuous lines, bounding canalicular spaces continuous below with the intercostal openings and above 

with the interseptal loculi high up. Costre granular. 

Septa crenulate or minutely denticulate. 
CRETACEOUS CORALS OF . THE ' GENUS MICRABACIA. 117 

Key to species of the genus Micrabacia.

1 

Costre absent in a sievelike central area of the base, which includes about 60 per cent of the basal diameter. Denticulations on septal edges ten to 1 millimeter .................... __ . M. cribaria Stephenson (p. 117, Pl . XX, figs. 1-3). 

Costre extending to center of base: 

Costre of last cycle long (20 to 30 per cent of diameter in adults), thick at terminus: 

Costre acute, denticulate: 

Costre 96 .................................... M. americana Meek and Hayden (p. 118, Pl. XX, figs. 4-5). 

Costre more than ?6- .. -............... M. americana var. multicostata Stephenson (p. 119, Pl. XX, fig. 6). 

Costre smooth. Denticulatwns on septal edges eight or nine to 1 millimeter. 

M. rotatilis Stephenson (p. 119, Pl. XXI, figs. 1-4). 

Costre faintly beaded. Denticulations on septal edges nine or ten to 1 millimeter. 

M. rotatilis var. georgiana Stephenson ([-. 120, Pl. XXI, figs. 5-8). 

Costre of last cycle short (7 to 18 per cent of diameter of base), thin at terminus: 

Costre subacute, distinctly denticulate: 

Denticulations of costre medium coarse. Corallum relatively high; sides steep. Denticulations on 

sep_tal ed~es ten to 1 millimeter .. : ......... ._. M. hilgardi Stephenson (p. 120, Pl. XXII, figs. 1-6). 

DentiCulatl?ns of costre coarserthanm M. hilgardi. Corallum large; sides evenly rounded. Septal edges 

alternate m prominence on the sides. Denticulations on septal edges ten to 1 millimeter. 

M. marylandica Stephenson (p. 121, Pl. XXII, figs. 7-10). 

Denticulations of costre coarse. Denticulations on septal edges twelve to 1 millimeter. Lengths of 

costre of last cycle more irregular and average length greater than in the two preceding species. 

M. mineolensis Stephenson (p. 122, Pl. XXIII, figs. 6-8). 

Costre flattish, faintly beaded: 

' Corallum low, sides straight, inclined inward. Denticulations on septal edges eleven or twelve to 1 

millimeter..- .. -.. -.................... M. mississippiensis Stephenson (p. 123, Pl. XXIII, figs. 9--11). 

Corallum high, sides nearly or quite vertical. Denticulations on septal margins seven to 1 millimeter. 

Micrabacia cribraria Stephenson, n. sp. 

Plate XX, figures 1-3. 

CoraJlum subdiscoidal; base nearly flat, 

upper surface convex, with axial depression 

slightly less than 1 millimeter deep. Dimensions of the type: Diameter 6.5 millimeters, 

height 2.5 millim3ters. 

The under side of the wall or base to a radial 

distance from the center of about 2 millimeters 

is irregularly tuberculated and presents numerous sievelike perforations roughly arranged in 

radial rows corresponding to the positions of 

the septa. The rough central area merges into 

a costate marginal band, the costre numbering 

96 and alternating with the septa. The costre 

· are thicker than the intercostal loculi are ' roughly tuberculated, and on the periphery 

project prowlike somewhat beyond the edges 

of t~e septa. In each intercostalloculus are synaptiCulre separated by elongated perforations. 

M. coronula Goldfuss (p. 124, Pl. XXIII, figs. 1-5). 

the columella; the two outer quaternaries of 

the group fuse against the tertiaries nearer the 

center than the two inner ones; the two outer 

quinaries of each of the two subgroups formed 

about the tertiaries fuse against the quaternaries nearer the center than the two inner 

quinaries of each subgroup. The primary 

septa are slightly higher than the members of 

the higher cycles, and their upper margins 

curve sharply downward into the central 

depression; the secondaries are slightly lower 

than the primaries, and the tertiaries, quaternaries, and quinaries each become progressively 

slightly lower. The margins of the septa are 

finely denticulate, the number being about ten 

to 1 millimeter. Synapticulre nre numerous; 

strire are present on the sides of the septre at 

the upper margins, apparently arranged fanlike, though only partly exposed .. 

Columella elliptical in cross section, spongy, 

trabecular, a certain number of the trabeculre 

terminating in more or less scattered, irregularly distributed papillre; length of cross 

section about one-fifth the diameter; width 

about one-tenth the diameter. 

This species differs from the other species of 

American Micra bacia in the arrangement of the 

basal costre, which instead of extending to the 1 ~xcluding the species M. beaumontii Milne-Edwards and Haime 

M . . (lttoni Duncan, and M.senoniensis BOlsche, thedescriptionso.fwhich center merge into a perforaUld, irregularly 

The septa are thin and form five complete 

cycles, arranged in six groups, one group in 

each of the interspaces between the six primaries. Total number of septa 96. The 

secondaries extend to the columella; the tertiaries fuse against the secondaries near 

are madequate. calcified, noncostate, sievelike area. 
118 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

Type.-Collection of the United States 

National Museum, catalogue No. 31996. From 

Whiteley Creek Landing, Neuse River, N. C. 

(5354). 1 

Distribution.- North Carolina: Snow Hill 

. marl member of Black Creek formation (upper 

part of Exogyra ponderosa zone), Whiteley Creek 

Landing,NeuseRiver (5354) ;Kerrs Cove, Black 

River (5362). Alabama: Lower part of Ripley 

formation (upper part of Exogyra ponderosa 

zone), Union Springs at'' ConecuhFalls" (6820); 

Central of Georgia Railway cut half a mile west 

of Union Springs (6815). Mississippi: Lower 

part of Selma chalk (upper part of Exogyra 

ponderosa ·zone), questionably on the Tupelo 

road 8 miles west of Fulton, Lee-County (6452). 

Micrabacia americana Meek and Hayden. 

Plate XX, figures 4-5. 

1860. Microbacia coronula. Meek and Hayden, Philadelphia Acad. Nat. Sci. Proc., vol. 12, p. 430 (not 

M. coronula, Milne-Edwards and Haime). 

1876. Micrabacia americana. Meek and Hayden, A report 

on the invertebrate Cretaceous and Tertiary fossils of the upper Missouri country: U. S. Geol. 

and Geog. Survey Terr. Rept., vol. 9, p. 1, pl. 28, 

figs. la-d. 

The description given in the second paper 

cited above is as follows: 

Corallum small, subplano-convex, or slightly concave 

below, and convex with a rather deep central depression 

above. Intercostal foramina of the mural disk oval and 

numerous. Rays or costre of the under side straight, 

about 12 in the middle, but bifurcating so as to number 

near 100 around the periphery, apparently denticulate. 

Septa few at the center, but increasing by the intercalation of smaller ones between, so as to equal the number 

of costre, with which they alternate on the periphery, very 

finely and sharply denticulate on the upper and lateral 

edges. 

This description can hardly be improved so 

far as the type material is concerned, but that 

material is so poorly preserved as scarcely to 

permit satisfactory identification of other 

material with it. The number of costre is 

probably 96 on the periphery, and the grouping of the costre and septa is probably the 

same as in all the species described in this 

paper, with the exception of M. americana var. 

multicostata, which has a greater number of 

costre and a slightly modified arrangement of 

the costre within the groups. 

Specimens from one locality in Wyoming 

and several localities in Montana, all from the 

1 Numbers in parentheses refer to United States Geological Survey 

collection numbers, unless otherwise indicated. 

upper part of the Montana group, are referred 

to this ·species, and one of them with well-preserved costre, associated in the same piece of 

rock with M. americana var. multicostata, is 

figured in Plate XX, figure 4. In this figured 

specimen the costre, which number 96, are 

arranged in six groups, 16 in a group; they 

are acute, becoming thicker on the periphery, 

and are distinctly and rather finely denticulate. The bifurcations of the separate cycles 

are at irregular distances from the center; 

the costre of the highest cycle are relatively 

long (1.5 to 2 millimeters), in this respect resembling those of M. rotatilis. The synapticulre in the intercostal loculi extending to the 

center number 12 or more and are separated 

by radially elongated perforations. The synapticulre and perforations are not definitely 

arranged in concentric rows. Other fragments 

in the same matrix indicate that the septa 

are thin and correspond in number to the 

costre, with which they alternate; on the sides 

of the septa are strire and rows of synapticulre 

and tubercles radiating fanlike from a point 

near the base of the columella. The septa are 

attached to the wall by a row of synapticulre 

that connect with the intercostal synapticulre. 

The strongly denticulate costre serve to dis-· 

tinguish this species from M. rotatilis and M. 

rotatilis var. georgiana, its nearest allies in the 

Coastal Plain. 

Type. -Collection of United States National 

Museum, Catalogue No. 456. From Moreau 

River, S. Dak. 

Occurrence.-Fox Hills sandstone, Moreau 

River, S.Dak. (U.S.N. M. catalogue No. 456); 

questionably identified from the Bearpaw 

shale, Forsyth project, sec. 26, T. 1 N., R. 

34 E., Montana (8133); questionably identified 

from the Pierre shale (upper part), 4 miles 

northeast of Moorcroft, Wyo. (7208); questionably identified from the Montana group 

(probably upper part), 20 miles southwest of 

Mingusville, Mont. (Homer Squyer collection, 

U. S. N. M. catalogue No. 22976); and from 

''Montana," probably from the Montana group 

(upper part), and perhaps from the locality 20 

miles southwest of Mingusville (Homer Squyer 

collection, U.S.N. M. catalogue No. 21896). 

Range.-Upper part of the Montana group, 

including the upper part of the Pierre shale and 

the Fox Hills sandstone. 
CRETACEOUS CORALS OF THE GENUS MICRABACIA. 119 

Micrabacia americana var. multicostata Stephenson, 

n. var. 

Plate XX, figure 6. 

This variety is based on one specimen 7 millimeters in diameter, showing only the under 

side of the wall (base). In the same rna trix 

are other specimens and fragments which probably belong to M. americana Meek and Hayden. 

The costre are acute, sharply defined, distinctly 

and finely denticulate and number 123 at the 

periphery; two costre fail to reach the margin, 

being suppressed or crowded out by adjacent 

ones. In general appearance the sculpture of 

the base resembles that of M. americana Meek 

and Hayden. The costre are separable into 

six groups, but the number of costre extending 

to the margins of the group is not uniform, 

some of the cycles not being complete. The 

number of costre in the six groups taken in succession about the disk are 22, 22, 20, 22, 19, 

and 18; one costa is crowded out in each of the 

last two groups. The bifurcations of each 

cycle are at very irregular distances from the 

center. The intercostal loculi are crossed by 

synapticulre, which in the loculi extending to 

the center number 12 or more. The synapticulre are separated by radially elongated perforations. 

This variety diff.3rs from aJl the known species of Micrabacia in that it possesses 123 

instead of 96 costre. The lack of uniformity in 

the number of costre in the groups and the 

obvious crowding out of one costa in each of 

two groups suggests that the type specimen 

may be abnormal. The fact that three of the 

six groups of costre number 22 suggests that 

the total number of costre in a normal specimen 

would be 132, though this would mean at least 

one incomplete cycle of costre. 

Type.-Collection of United States National 

Museum, catalogue No. 31997. 

Occurrence.-Cretaceous of" Montana," probably from the upper part of the Montana group, 

and perhaps from the locality 20 miles southwest of Mingusville (Homer Squyer collection). 

Micrabacia rotatilis Stephenson. 

Plate XXI, figures 1-4. 

1916. Micrabada rotatilis. Stephenson, Maryland Geol. 

Survey, Upper Cretaceous, pp. 753-755, pl. 49, 

figs. 1-4. 

Corallum subdiscoidal; moderately high, with 

fiat to rather strongly concave base; sides steep 

below, rounding evenly into the subflattish top; 

axial depression 1.5 to 2 millimeters deep. 

Dimensions of the type: ·Diameter 9 millimeters, height about 4 millimeters. 

The costre on the base are thin and sharply 

defined and alternate with the septa; they start 

with six at the center and by successive bifurcations increase to 96 on the periphery; they 

are nearly smooth and increase slightly in thickness from the oenter to the periphery. The 

costre are in six groups corresponding to the 

groups of septa. Each group starts with one 

costa (first cycle), which bifurcates near the 

center to form two costre (second oycle); these 

bifurcate 0.5 millimeter from the center to 

form four costre (third cycle); the four bifurcate about 1 millimeter from the center and produce eight costre (fourth cycle); imd the eight 

bifurcate 1.5 to 2 millimeters frOin the center, 

producing 16 costre (fifth cyle); in the last cycle 

the bifurcations producing the two outer and 

the two middle pairs of the group take place 

nearer the center than those of the other four 

pairs; in the largest specimens the pairs of 

costre in the last cycle are 2.5 to .3 millimeters 

long. The ends of the costre are prowlike but 

scarcely project beyond the edges of the septa. 

The intercostal loculi are narrow and are crossed 

by small synapticulre separated by radially 

elongated perforations; in the type the perforations in the intercostal loculi extending to the 

center number 18; the intercostal synapticulre 

and perforations are roughly arranged in concentric rows. 

The septa are thin and form five complete 

cycles arranged in six groups, one group in each 

of the interspaces between the primary septa. 

Total number of septa 96. The secondaries 

extend to the columella; the tertiaries fuse 

against the secondaries near the columella; the 

two outer quaternaries of the group fuse against 

the tertiaries nearer the center than the two 

inner ones; the two outer quinaries of each of 

the subgroups formed about the tertiaries fuse 

against the quaternaries nearer the center than 

the two inner ones. The primary septa are a 

little higher than_ the members of the higher 

cycles, and the septa of each of the succeeding 

cycles appear to be a little lower than those of 

the preceding cycles. The edges of the septa 

are finely and distinctly denticuls,te, the number of denticulations being eight or nine to 1 

millimeter; the inner edges of the primaries and 
120 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

secondaries are bifid, each presenting a troughlike depression with serrated margins descending to the top of the columella; sides of septa 

with strire, tubercles, and rows of synapticulre 

radiating fanlike from a point near the base of 

the columella. Each septum is joined to the 

wall (base) by synaptioulre .that connect with 

the intercostal synapticulre. These are separated by perforations that connect with the 

intercostal perforations. 

Columella elliptical in cross section, spongy, 

trabecular, some of the trabeculre terminating 

above in more or less scattered, irregularly distributed small papillre; length of cross section 

about one-sixth the diameter; width about onetwentieth the diameter. 

This species differs from other species of 

Micra bacia from the Coastal Plain in the greater 

sharpness and smoothness of the basal costre, 

the greate;r irregularity in the distance of tho 

bifurcations of the sev6ral cycles from tho 

center, the greater length of the costre of the 

last cycle, the greater number of intercostal 

perforations, and the greater size attained by 

the adults. It is distinguishable from M. 

rotatilis var. georgiana by its smoother ·-and 

slightly thicker cos too. M. · americana Meek 

and Hayden and its variety, multicostata, have 

more strongly denticulate bases. In M. coronula (Goldfuss), of the European Cretaceous, 

the denticulations of the septal edges are 

markedly coarser than those of any of the 

American species. 

Type.-Collection of the Maryland Geological Survey, on deposit in the United States 

National Museum. From a locality seven ... 

eighths of a mile southwest of Brightseat, Md. 

Distribution.-Prince Georges County, Md., 

Monmouth formation (Exogyra costata zone), 

bed of small branch about seven-eighths of a 

mile southwest of Brightseat and threeeighths of a mile south of the Sheriff road; 

near MoNeys · Corners, about a mile west of 

Friendly; questionably near Seat Pleasant. 

Range.-The three localities enumerated are 

within the Exogyra costata zone. 

Micrabacia rotatilis var. georgiana Stephenson, n. var. 

Plate XXI, figures 5-8. 

This variety is based on four nearly complete 

specimens and several fragments from Mercers 

Mill C;reek near Georgetown, Quitman County, 

Ga., which possess most of the specific chara~-

ters of M. rotatilis except that the costre are 

thinner and sharper, producing a more open 

effect, and instead of being nearly smooth are 

rather faintly denticulated, though strongly 

enough to produce a rougher appearance than 

that of the more typical members of the 

species. The synapticulre on the sides of the 

septa seem also to be a little coarser, and there 

is a tendency for the strire to be replaced by 

rows of small tubercles. The number of denticulations on the margins of the septa is nine 

or ten to 1 millimeter. Dimensions of the 

type (Pl. XXI, figs. 5-7): Diameter, 6.5 

millimeters; height, 2.75 millimeters. 

Type.-Collection of United States National 

Museum, catalogue No. 31998. 

Occurrence.-Upper part of Ripley formation (upper part of Exogyra costata zone), 

Mercers Mill Creek near Georgetown, Quitman 

County, Ga. (5417). 

Micrabacia hilgardi Stephenson, n. sp. 

Plate XXII, figures 1-6. 

. Corallum somewhat variable, but in general 

moderately high, subdiscoidal, with steep, only 

slightly convex sides, suggesting a truncated 

cone; base fiat, slightly convex or slightly concave; .axial depression small and about 1 millimeter deep in the type, with steep sides. 

Dimensions of the type (Pl. XXII, figs. 4-6): 

Diameter 5.5 millimeters, height 3 millimeters. 

The costre on the base or wall start with six 

and by successive bifurcations reach 96 on the 

periphery; they alternate with the septa. 

Each of the six original costre (first cycle) is 

the focus of a group; the original divides near 

the center into two (second cycle); these split 

about 0.5 millimeter !:rom the center to form 

four (third cycle); the four split 1.25 to 1.5 

millimeters from the center to form eight (fourth 

cycle); and finally the eight split on the periphery to form 16 (fifth cycle). The bifurcations 

of each cycle are at rather markedly irregular 

distances from the center. Up to the fourth 

cycle the costre are coarsely denticulate; those 

of the last cycle are thin, sharp, and &ely denticulate, and form a narrow band bordering the 

periphery; they project slightly beyond the 

periphery. In the .narrow intercostal loculi 

are synapticulre numbering 12 ·in the loculi 

extending to the ce:p.ter, separated by slightly 

elongated perforations; the intercostal synap-:-
CRETACEOUS CORALS OF THE GENUS 'MICRABACIA. 121 

ticulre and perforations are arranged in concentric rows. 

The septa are thin and are separable into six 

groups, each group occupying the interspace 

between two of the six primaries. Total 

number of septa 96. 'fhe secondaries extend 

to the columella; the tertiaries are fused 

against the secondaries near the columella; 

the two outer quaternaries of each group are 

fused against the tertiaries nearer the center 

than the two inner ones; and the two outer 

quinaries of each subgroup formed about the 

tertiaries are fused against the quaternaries 

nearer the center than the two inner ones. 

The primary septa are slightly higher than the 

secondaries, and their inner edges descend 

steeply to the top of the columella; the members of each of the succeeding cycles are slightly 

lower than those of the preceding cycles. Margins of the septa finely denticulate, the denticulations numbering about twelve to 1 millimeter. 

Sides of septa with strire, tubercles, and synapticulre radiating fanlike from a point near the 

base of the columella. Each septum is joined 

to the wall · (base) by synapticulre that connect 

with the intercostal synapticulre; these are 

separated by perforations that connect with 

the intercostal perforations. 

Columella elliptical, spongy, trabecular, certain of the trabeculre terminating above in 

more or less scattered, irregularly distributed 

papillre; length of the cross section a little less 

than one-fifth the diameter; width a little less 

than one-tenth the diameter. 

This species differs from M. marylandica in 

size and form, being smaller and having 

straighter sides, which incline slightly more 

toward the center; the costre are not quite so 

thiok, the costal denticulations are a little 

finer, the bifurcations of the separate cycles 

are at more irregular distances from the center, 

and the edges of the septa on the sides of the 

corallum do not alternate in prominence. In 

M. cribraria the corallum is flatter and only the 

outer cycle of basal costre are clearly distinguishable, the other cycles being obscured by 

calcification; in M. rotatilis the corallum is 

flatter and the costre are thinner, sharper, and 

much smoother, and the costre of the last cycle 

are much longer; in M. americana Meek and 

Hayden the corallum is flatter, the basal costre 

are thinner, and the costre of the last cycle are 

much longer and not so thin at the extremities; 

in M. mississippiensis the corallum is flatter, 

the basal costre are thinner and smoother, and 

the bifurcations of the separate cycles are at 

less regular distances from the center. In the 

European species M. coronula (Goldfuss) the 

denticulations on the margins of the septa are 

markedly coarser. 

Type.-Collection of United States National 

Museum, catalogue No. 32001. From Lee's 

old mill site, Union County, JMiss. (6873). 

Named in honor of Prof. E. W. Rilgard, former 

State geologist of Mississippi. 

Distribution.-Mississippi: Ripley formation 

(Exogyra costata zone), Lee's old mill site, 2 

miles northeast of Keownville, ·union County 

(6873). Chattahoochee region: lJpper part of 

Ripley formation (Exogyra costata zone), 

Eufaula, Ala. (854); Mercers Mill Creek near 

Georgetown, Ga. (5417); Chattahoochee River, 

2 miles below Eufaula (857). 

Range.-Exogyra costata zone. 

Micrabacia marylandica Stephenson. 

Plate XXII, figures 7-10. 

1916. Micrabacia marylandica. Stephenson, Maryland 

Geol. Survey, Upper Cretaceous, pp. 755-757, pl. 

48, figs. 1-4. 

This species is based on seven good specimens and a few fragments from the Monmquth 

formation of Maryland. 

Corallum low to moderately high; subdiscoidal, base flat or slightly convex, top evenly 

convex with a small axial depression about 1.25 

millimeters deep in the type. Dimensions of 

the type (Pl. XXII, fig. 10): Di3.meter 7 millimeters, height 3 millimeters. 

The under side of the base or wall is O:rllamented with a system of radiatmg bifurcating 

costre which alternate with the septa; the system starts with six costa, which by successive 

bifurcations form cycles of 12, 24, 48, and 96 

costre. Each of the original six: costre (first 

cycle) is the focus of a group; the original of 

each group splits near the center into two (second cycle); these split 0.5 millin1eter from the 

center into four (third cycle); about 1.5 to 1.75 

millimeters from the center the four costre 

divide, to form eight (fourth cycle); and about 

2.5 millimeters . from . the center in the type 

the eight divide, producing H> costre (fifth 

cycle) on the outer rim. The bifurcations of 

each cycle are at nearly equal distances from 

the center. The costre up to the fou;rth cycle 
122 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

are relatively thick and coarsely nodular; 

those of the last cycle are thin, finely denticulate, and form a band about 0.75 millimeter 

wide, bordering the outer margin; they appear not to project beyond the edges of the 

septa. The intercostal loculi are very narrow 

and are occupied by 12 or 13 synapticulre separated by perforations, most of which are slightly 

elongated radially; the synapticulre and perforations. are arranged in concentric rows. 

The septa are very thin and are arranged in 

six groups, one group in each of the interspaces 

between the primary septa. Total number of 

septa 96. The secondaries extend to the 

columella; the tertiaries fuse against the 

secondaries near the columella; the two outer 

quaternaries of the group fuse against the 

tertiaries nearer the center than the two inner 

ones; in each of the two subgroups formed 

about the tertiaries the two outer quinaries 

fuse against the quaternaries nearer the center 

than the two inner ones. The primary septa 

are slightly higher than the members of the 

higher cycles, which appear to be of about 

equal height. On the sides of the corallum 

the septa distinctly alternate in prominence. 

Margins of the septa finely denticulate, the 

number of denticulations being about ten to 1 

millimeter. Sides of septa with strire and 

rows of synapticulre and tubercles radiating 

from a point near the base of the columella. 

Columella elliptical, spongy, trabecular, some 

of the trabeculre terminating in more or less 

scattered, irregularly distributed, small papillre; 

length of cross section between one-fifth and 

one-sixth the diameter; width about one-tenth 

the diameter. 

Micrabacia hilgardi differs from this species 

in size, form, and ornamentation of the base; 

its corallum is smaller, the sides straighter 

and more inclined, and the septal edges on the 

sides of the corallum do not alternate in prominence; the bifurcations of its separate cycles 

of costre are at more irregular distances from 

the center, and the costre are thinner and more 

finely denticulate. In M. cribraria the costre 

and perforations of the base are largely 

obscured by irregular calcification, and the 

costre project more prominently on the periphery. In M. mississippiensis the basal costre 

are narrower, smoother, and flatter, the bifurcations of each cycle are more irregularly 

spaced with reference to the center, and the 

profile of the side of the coraUum is not so 

steep and is slightly truncated. In M. rotatilis 

the basal costre are thinner, sharper, and 

much smoother. In M. americana Meek and 

Hayden. the costre are narrower and sharper, 

and the bifurcations producing the last cycle 

are much nearer the center and at less regular 

distances from the center. In M. coronula 

(Goldfuss) the corallum is higher and the 

septal denticulations coarser. 

Type. -Collection of the Maryland Geological Survey, on deposit in the United States 

National Museum. Found seven-eighths of a 

mile southwest of Brightseat, Prince Georges 

County, Md. 

Occurrence.~Monmouth formation .(Exogyra 

costata zone), bed of small branch seven-eighths 

of a mile southwest of Brightseat and threeeighths of a mile south of the Sheriff road, 

Prince Georges County, Md.; half a mile west of 

Friendly, Prince Georges County, Md. 

Micrabacia mineolensis Stephenson, n. sp. 

Plate XXIII, figures 6-8. 

The description of this species is based on 

two imperfect specimens, of which the one 

shown in Plate XXIII, figure 6, is taken as the 

type. 

The corallum is crushed in both specimens 

but appears to be of moderate height, with 

steep to nearly vertical, gently convex sides; 

axial depression of moderate size and about 

0.75 millimeter deep in the type; base slightly 

concave in both specimens. Dimensions of the 

type: Diameter 5.5 millimeters, height 2.5 

millimeters ( n. 

The costre on the base start with siX at the 

center and by successive bifurcations reach 96 

on the periphery; they alternate with the septa. 

The costre are in six groups, each group having 

as its focus one of the original six costre (first 

cycle); the original divides near the center into 

two (second cycle); the two divide about 0.5 

millimeter from the center to form four (third 

cycle); these divide abbut 1 to 1.25 millimeters 

from the center to form eight (fourth cycle); 

and the eight divide 1.25 to 2 millimeters from 

the center to form 16 (fifth cycle). The costre 

of the ·fifth cycle are 0.75 to 1.5 millimeters 

long. The bifurcations forming the costre of 

the third, fourth, and fifth cycles are at rather 

markedly irregular distances from the center. 

Up to and including the fourth cycle the costre 
CR.ETACEOUS CORALS OF THE GENUS MICRABACIA. 123 

are thick and coarsely denticulate; those ofthe 

fifth cycle are thin, sharp, and finely denticulate 

and project a little beyond the edges of the 

septa. The interseptal synapticuhe, which 

number 12 or 13 in the loculi extending to the 

center, are separated by- radially elongated 

perforations. 

The septa are thin and are separable into six 

groups, each group occupying the interspace 

between two of the six primaries. Total number of septa 96. The secondaries extend to the 

columella; the tertiaries fuse against the secondaries near the columella; the two outside 

quaternaries of each group fuse against the tertiaries nearer the center than the two inner 

quaternaries; and the two outside quinaries of 

each subgroup formed about the tertiaries are 

fused against the quaternaries nearer the center 

than the two inner ones. The primary septa 

are slightly more prominent than the secondaries, their inner edges descending steeply to 

the top of the columella; the members of each 

of the succeeding cycles appear to be slightly 

lower than those of the preceding ones. Margins of the septa finely denticulate, the beads 

numbering 12 to 1 millimeter. Sides of septa 

not uncovered. 

C~lumella elliptical, the length of the cross 

section at the top being about one-fifth the 

diameter and the width about one-tenth the 

diameter. The columella is spongy and trabecular, certain of the trabeculre terminating 

above in mme or less scattered, irregularly distributed papillre. 

This spec~es is most nearly related to M. 

hilgardi and M. marylandica, from which it 

may be distinguished by its coarser and more 

roughly denticulated base and by the greater 

average length of the costre of the last cycle. 

Type.-Collection of United States National 

Museum, catalogue No. 32006. 

Occurrence.-Probably Navarro formation 

(Exogyra costata zone), well of Hoard Oil & Gas 

Co., 7 miles east of Mineola, Wood County, 

Tex.; collected at a depth of 3,146 to 3,160 feet 

(9369). 

Micrabacia mississippiensis Stephenson, n. sp. 

Plate XXIII, figures 9-11. 

This species is based on one specimen from 

the Ripley formation of Mississippi. Corallum low, subdiscoidal, with flat base, moder308300-17-9 

ately steep, slightly convex sides, and axial 

depression about 0.75 millimeter deep. Dinlensions: Diameter, 6 millimeters; height, 2 

millimeters. 

Under side of wall (base) ornamented with ' 

sharply defined, moderately thick, flattish, 

coarsely but rather faintly nodular costre 

which alternate with the septa; they start 

"\vith six at the center and by successive bifurcations reach 96 on the periphery. Each 

of the original six costre is the center of a 

group. The original (first cycle) of the group 

divides near the center into two (second cycle), 

and these divide to form four (third cycle) at 

less than 0.5 millimeter from the center; of 

the four costre the two outside ones divide 

about 1 millimeter and the two inside ones 

about 1.5 millimeters from the eenter, forming eight (fourth cycle); of the eight costre the 

two outside ones divide about 1.76 millimeters, 

the two middle ones about 2.25· millimeters, 

and the other four about 2.5 millimeters from 

the center, forming 16 (fifth cycle). The distances of the bifurcations of each cycle from 

the center are thus rather markedly irregular. 

The costre of the last cycle are thinner than 

those of the lower cycles, their ends are 

prowlike, and they project slightly beyond 

the septa. The narrow intercostal loculi are 

crossed by concentrically arranged synapticulre numbering 12 or 13 in the loculi extending to the center; the synapticu1re are separated by radially elongated perforations. 

The septa ate thin and are arranged in six 

groups with six primaries and four complete 

higher cycles, making a total of 96 on the 

periphery. Each group occupies one of the 

interspaces between two of the primaries. 

The secondaries extend to the columella; the 

tertiaries are fused to the secondaries near the 

columella; the two outside quaternaries of 

each group are fused to the tertiaries nearer the 

center than the two inner ones; in each of the 

subgroups formed about the tertiaries the two 

outer quinaries are fused against the quaternaries nearer the center than the two inner 

ones. The primary septa are slightly higher 

than the members of the higher cycles, and 

those of each of the succeeding cycles are 

slightly lower than those of the preceding 

cycles. The margins of the septa. are set with 

beadlike denticulations, the number being 

about 11 or 12 to 1 millimeter. The inner 
124 SHORTER CONTRIBUTIONS TO GENERAL GEOLOGY, 1916. 

edges of the primaries where they descend to 

the top of the columella are set with a double 

row of denticulations. The sides of the septa 

are not well exposed except in one small area 

· near the top, on which are rows of prominent 

tubercles radiating fanlike from within. 

Columella elliptical in cross section, spongy, 

trabecular, some of the trabeculre terminating in more or less scattered, irregularly distributed nodular processes. Length of cross 

section about one-sixth the diameter; width 

about one-tenth the diameter. 

The other American species of Micrabacia 

differ from this species in the following characters: In M. cribraria the irregular calcification 

has obscured all but the last cycle of basal 

costre; the corallum of M. hilgardi is higher, the 

sides are steeper, and the costre of the last 

cycle are shorwr; in M. marylandica the bifurcations of the separate cycles of costre are at 

more regular distances from the center, and 

the average length of the costre of the last 

cycle is less; in M. americana Meek and 

Hay-den and M. rotatilis the costre are thinner 

and sharper, and the costre of the last cycle are 

markedly longer. The septal denticulations of 

M. coronula (Goldfuss) of the European Cretaceous are coarser than in any of the American species. 

Type.-Collection of United Staws National 

Museum, catalogue No. 32008. 

Occurrence.-Ripley formation (Exogyra costata zone), Lee's old mill site, 2 miles northeast 

of Keownville, Union County, Miss. (6873). 

Micrabacia coronula ( Goldfuss ). 

Plate XXIII, figures 1-5. 

1826. Fungia coronula. Goldfuss, Petrefacta Germanire, 

vol. 1, p. 50, pl. 14, fig. 10. 

1840. Fungia coronula. F. A. Roemer, Die Versteinerungen des norddeutschen Kreidegebirges, p. 25. 

1849. Micrabacia coronula. Milne-Edwards and Haime, 

Compt. Rend., vol. 29, p. 71. 

1850. Micrabacia coronula. Milne-Edwards and Haime, A 

monograph of the British fossil corals, p. 60, pl. 

10, figs. 4, 4a-c (with a synonymy), Paleontographical Society. 

1860. Micrabacia coronula. Milne-Edwards, Histoire naturelle des coralliaires, vol. 2, p. 29 (with synonymy). 

.1862. Fungia coronula. Goldfuss, Petrefacta Germanire, 

2d ed., vol. 1, p. 47, pl. 14, fig. 10. 

1884. Micrabacia. Duncan, Linnean Soc. London Jour., 

Zoology, vol. 18, p. 143. 

1905. Micrabacia. Vaughan, U. S. Nat. Mus. Proc., vol. 

28, p. 387 (Duncan's description quoted). 

An account and illustrations of Micrabacia 

coronula (Goldfuss) are included for purposes 

of reference and comparison. The description of Milne-Edwards and Haime is quoted in 

full below: 

Corallum simple, lenticular, short; its under surface 

horizontal or slightly concave; its upper surface somewhat 

convex. Mural disk completely naked and regularly 

perforated by small intercostal pores. Costre closely set, 

almost straight, equally narrow, not prominent, and but 

slightly echinulated; only 12 of them arise in the center 

of the disk, but these soon bifurcate, and the 24 costre so 

formed soon divide again; at about half the distance from 

the center to the circumference of the disk each costa 

bifurcates once more, and the two terminal costre so 

formed are grouped two by two toward the periphery of 

the disk. The granulations which form all these costre are 

not very distinct and are arranged in single lines. Calicular fossula small and not very deep, but well marked anc;I 

rather elongated laterally. Columella very small, oblong, 

and subpapillose. Septa forming five complete cycla, 

and corresponding to the intercostal spaces; those of the 

last cyclum quite rudimentary; the . others tall, thin, 

straight, and united · by subspiniform trabiculre. Those 

of the first cyclum larger than the others and augmenting 

slightly in thickness toward the middle; the secondary 

ones almost as large; all delicately denticulated along their 

upper edge, and much thinner toward their outer and 

inferior angle than in any other part. Diameter, three or 

sometimes four lines; height, one line and a half. 

The above-described fossils were found in the Greensand at Warminster, in Wiltshire, and according to William Smith, who was the first author that mentions this 

fossil, are also met with at Chute Farm and Puddle Hill, 

near Dunstable. 

By an attentive comparison with the specimens decribed by Goldfuss and belonging to the Poppelsdorff 

Museum at Bonn, we have ascertained tl;le specific identity of this British co:r:al with the Fungia coronula found in 

the chalk of Essen. Specimens exist in Mr. Bowerbank's 

cabinet and in the collections belonging to the Geological_ 

Society, the Museum of Paris, the Museum of Bonn, and 

M. Defrance at Sceaux, who has designated it by the unpublished name of Fungia dubia. 

Duncan's description of the genus, which 

amounts to a nearly complete description of 

the species, is quoted on page 116. To these 

descriptions I may add that, as in the American species, the septa probably start with six 

instead of 12, and by successive intercalations 

in four additional complete cycles increase to 

96 in the adult. Likewise the basal costre 

start with six and by successive bifurcations in 

five complete cycles reach 96 on the periphery. 

Compared with the American forms the denticulations on the edges of the septa are somewhat coarser (seven to 1 millimeter), the axial 

depression is shallower, the adults attain a 

larger size, and, though somewhat variable in 
CRETACEOUS CORALS OF THE GENUS MICRABACIA. 125 

form, the profile is in general more nearly verti- (7971), and about 3 miles southeast of Moorcal on the sides. croft, Wyo., approximately 75 feet below the 

The specimens in the two lots indicated be- Fox Hills sandstone (6520); Montana group 

low, which are supposed to be typical of M. (upper part), Old Cooper Creek Crossing, Laracoronula (Goldfuss), are in very different states mie Plains, Wyo. (U. S. N. M. catalogue No. 

of preservation; those from the British Mu- 28528); Montana group (upper part), Ben 

seum are filled with matrix; those from Hoi- Gaugh's ranch, Cooper Creek, 20 miles northland are free from matrix:, but the costre are west of Laramie, Wyo. (3479). 

missing and the margins of the septa are im- Specimens of Micra bacia referred by W eller1 

perfe?t, so t~at they are scarcely specifically I to M. ?'mericana Meek and Hayd~n have .b~en Identifiable with the other material. found m New Jersey at the followmg localities: 

Distribution.-According to Goldfuss the Merchantville clay, near Matawan; Woodspecies occurs in the "Mergelgrand" at Essen, bury clay, Lorillard, near Matawan and near 

Prussia, and Milne-Edwards and Haime state Haddonfield; Wenonah sand, near Crawfords 

that in England it occurs in the [upper] Green- Corner. 

sand (Albian). (See quotation, p. 124.) Milne- Through th~ courtesy o~ Dr. H. B. Kii.mmel 

Edwards gives the occurrence and distribution I have exammed Weller s figured specrmens 

as "Group de la craie tu:ffeau: Le Maus, Essen, from the Woodbury clay near Lorillard, and 

Warminster." Specimens in the collection of the lots fr~m the Woodbury clay and from ~he 

the United States National Museum are Merchantville clay near Matawan, all of which 

labeled as follows: appear to be too poorly preserved for satisfacU. S. N. M. Cat. No. 155214. Folx-les-Caves, Holland, 

Cretaceous, Group de la craie tuffeau. 

U. S. N. M. Cat. No. 156436. Obtained from the BritiEh 

Museum (no locality given). 

Three specimens from the first locality, 

figured on Plate XXIII, figures 3, 4, and 5, are 

renumbered catalogue Nos. 32002 and 32003; 

two specimens from the second lot, figured on 

Plate XXIII, figures 1 and 2, are renumbered 

catalogue Nos. 32004 and 32005. 

UNIDENTIFIED SPECIMENS OF MICRABACIA. 

tory specific identification. Squeezes' made 

from prints of the bases of the specimens from 

Lorillard suggest the type of sculpture exhibited by M. cribraria rather than that of M. 

amencana. 

Dr. Weller states, in a letter recently received, that the material from Haddonfield 

examined by him was in the collection of the 

Academy of Natural Sciences of Philadelphia. 

Dr. H. A. Pilsbry, in response to a letter of inquiry, states that he can not find these specimens in the collection, and apparently they 

I have been lost, a most unfortunate circumSpecimens of Micrabacia too poorly pre- stance, because, according to Dr. Weller, they 

served for satisfactory specific identification were preserved intact, and not in the form of 

have been found in the western interior at the molds, as were the other New Jersey specimens. 

following localities: Pierre shale (upper part), 5 miles southwest of Marmarth. N. Dak. 1 Weller, Stuart,, Cretaceous paleontology of New Jersey: New Jersey Geol. Survey, Paleontology, vol. 4, p. 271, pl. 5, figs. 14-17, 1907. 

PLATES XX-XXIII. 

127 
PLATE XX. 

Micrabacia cribraria Stephenson, n. sp. (p. 117). 

FIGURE 1. Calicular view of the type, X 4, from the Snow Hill marl member of the Black Creek formation (upper 

part of E xogyra ponderosa zone), Whiteley Creek Landing, Neuse River, N. C. (U.S. G. S. collection 

5354; U.S.N. M. catalogue No. 31996.) The periphery and margins of all the septa are imperfect. 

2. Side view of the type, X 8; the upper portions of the septal edges are imperfect. 

3. Basal view of the type, X 8; the ends of the costre and portions of the surface are imperfect. 

Micrabacia americana Meek and Hayden (p. 118). 

FIGURE 4. Basal view of a specimen, X 8, from "Montana," probably from the upper part of the Montana group, and 

perhaps from a locality 20 miles southwest of Mingusville. (Homer Squyer collection, U. S. N. M. cata 

Iogue No. 21896.) 

5. View of a broken specimen in the same collection, partly restored by retouching, showing the profile through 

the center and faint. indications of the characters on the sides of the septa. (U.S.N. M. catalogue No. 

21896.) 

Micrabacia americana var. multicostata Stephenson, n .. var. (p. 118). 

FIGURE 6. Basal view of the type, X 8, from "Montana," probably from the upper part of the Montana group, and 

perhaps from a locality 20 miles southwest of Mingusville. (Homer Squyer collectiOA, U.S.N. M. catalogue No. 31997.) 

128 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE XX 

2 

1 

5 

3 

4 

6 

SPECIES OF MICRABACIA. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE XXI 

7 

6 

2 

1 

4 8 

SPECIES OF MICRABACIA. 
PLATE XXI. 

Micrabacia rotatilis Stephenson (p. 119). 

FIGURE 1. Calicular view of the type, X 4, from the Monmouth formation (Exogyra costata zone), bed of a small branch 

about seven-eighths of a mile southwest of Brightseat, and three-eighths of a mile south of the Sheriff road, 

Prince Georges County, Md. (Collection of the Maryland Geological Survey, on deposit in the United 

States National Museum.) The septal edges are imperfect and the interseptal loculi are filled with 

matrix. 

2. Side view of the type, X 8; the interseptal loculi are filled with matrix and the upper part of the corallum 

is imperfect. 

3. Vertical internal cross section of the type, X 8; broken through the center, showing the sides of septa, the 

spongy columella, and the intercostal perforations of the base. 

4. Basal view of the type, X 8, showing the character and grouping of the costre. 

Micrabacia rotatilis var. georgiana Stephenson, n. var. (p. 120). 

FIGURE 5. Calicular view of the type, X 4, from the upper part of the Ripley formation (Exogyra costata zone), Mercers 

Mill Creek near Georgetown, Ga. (U.S. G. S. collection 5417; U.S.N. M. catalogue No. 31998.) The 

upper edges of the septa are imperfect. 

6. Side view of the type, X 8; the interseptal loculi are filled with matrix, and the upper part of the corallum 

is imperfect. 

7. Basal view of the type, X 8, showing the character and grouping of the septa. 

8. Vertical internal cross section of a fragmentary specimen from the type locality (U.S. G. S. collection 5417; 

U.S.N. M catalogue No. 31999), showing the side of a septum and the intercostal perforations of the base. 

129 
PLATE XXII. 

Micrabacia hilgardi Stephenson, n. sp. (p. 120). 

FIGURE 1. Calicular view, X 4, of a specimen from the upper part of the Ripley formation (Exogyra costata zone), 

Mercers Mill Creek near Georgetown, Quitman County, Ga. (U. S. G. S. collection 5417; U. S. N. M. 

catalogue No. 32000.) ,The upper edges of the septa are imperfect. 

2. Side view of the same specimen, X 8, showing the septal margins and the prowlike ends of the costre. 

3. Basal view of the same specimen, showing the character and grouping of the costre. 

4. Calicular view of the type, X 4, from the Ripley formation (Exogyra costata zone), Lee's old mill site, 2 

miles northeast of Keownville, Union County, Miss. (U.S. G. S. collection 6873; U.S.N. M. catalogue 

No. 32001.) The edges of the septa are imperfect and the interseptal loculi are filled with matrix. 

5. Side view of the type, X 8, showing the septal edges and the prowlike ends of the costre. 

6. Basal view of the type, X 8, showing the character and grouping of the costre. 

Micra bacia marylandica Stephenson (p. 121 ). 

FIGURE 7. Calicular view of a specimen, X 4, from the Monmouth formation (Exogyra costata zone), bed of a small 

branch about seven-eighths of a mile southwest of Brightseat, and three-eighths of a mile south of the 

Sheriff road, Prince Georges County, Md. (Collection of the Maryland Geological Survey, on deposit in 

the United States National Museum.) The edges of the septa are imperfect and the interseptal loculi 

are filled with matrix. 

8. Side of the same specimen, X 8, showing the septal edges and the prowlike ends of the costre. 

9. Vertical cross section of a specimen, X 8, in the same collection, showing the sides of the septa, the spongy 

columella, and the intercostal perforations of the base. 

10. Basal view of the type, X 8, in the same collection, showing the character and grouping of the costre. 

130 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE XXII 

1 

2 

3 

4 

5 

6 

9 7 

8 

10 

SPECIES OF MICRABACIA. 
U. S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 98 PLATE XXIII 

1 3 4 

9 

2 

10 

7 

6 

11 8 

SPECIES OF MICRABACIA. 
PLATE D:III. 

Micrabacia coronula (GoMfuss) (p. 124). 

FIGURE 1. Side view of a specimen, X 4, from the British Museum. locality not stated on the label. The septal edges 

are imperfect and the interseptal loculi are filled with matrix. (U. S. N. M. catalogue No. 32004.) 

2. Basal view of a specimen, X 4, from the same locality. (U.S.N. M. catalogue No. 32005). The costre are 

very much worn and imperfect. 

3, 4. Ca.Iicular view and basal view, X 4, of a specimen fmm the "Cretaceous, Group de la craie tuffeau, Folxles-Caves, Holland." (U. S. N. M. catalogue No. 32002.) The edges of the septa are imperfect, and 

the costre are gone from the base, leaving only the lower edges of the septa showing. 

5. Side view of a specimen, X 4, from the same locality. (U.S.N. M. catalogue No. 32003.) The ends of 

the costre are missing. 

Micrabacia mineolensis Stephenson, n. sp. (p. 122). 

FIGURE 6. B~sal vlew of the type, X 8, from the Navarro formation (?), well of Hoard Oil & Gas Co., 7 miles east 

of Mineola, Wood County, Tex., collected at a depth of 3,146-3,160 feet. (U. S. G. S. collection 9369; 

U. S. N. M. catalogue No. 32006.) Shows the c!w,racter and grouping of the costre. 

7. Calicular view of a crushed specimen, X 4, in the E;ame collection. (U. S. N. M. catalogue No. 32007.) 

8. Side view of the specimen illustrated in figure 7; shows the septal edges and the prowlike ends of the basal 

costre. 

FIGURE 9. 

10. 

11. 

Micrabacia mississippiensis Ste1•henson, n. sp. (p. 123). 

Calicular view of the type, X 4, from the Ripley formation (Exogyra costata zone), J..~ee's old mill site, 2 

miles northeast of Keownville, Union County, .MiE.s. (U.S. G. S. collection 6873; U.S.N. M. catalogue 

No. 32008.) The upper edges of the septa are imperfect. 

Side view of the type, X 8, showing the septal edges and the prowlike ends of the costre. 

Basal view of the type, X 8, showing the character :a.nd grouping of the costre. 

131