New-York daily tribune. [volume] (New-York [N.Y.]) 1842-1866, 1847-11-01

Now here we have a blvalve with two symlnet
rical shells. Here is the gament uniting the t~o
valves and here some tuberces on the edge Of the
valve which are usually but incorrectly called
teeth. They are by no means teeth. They are
merely serratures OF dentations. Here is the mar
gin of the shell by which the two valves unite more
strongly, this portion Of the shell has been called
the hinge.
Now this being the anterior extremity where
the mouth is placed this will be the pOsteriOr ex
tremity. aud we will have animal walking with
the aid Of It's feet in upright position. the mouth
forward. the feet downward the right and lei.
hand In an equilibrium on the right and ieit
hand side and the back upward-the posterior
being backward. But IN the oyster, when the
two parts are compared with one another, IN
such an animal we will find that no longer is the
position maintained. but the animal through life
lies fat on one side from the beginning The young
oyster lies on one side ofthe egg begins 70 gro" IN
tha, position and never comes 20 have the anterior
extremity forward and the aides ia equal position.
One side the left. remains below. aud the night IN
the form Of a cover upward, resting upon the lower
side.
Now in the oy ster the anterior and posteror mar
gins Of the pDimal are not equal nor are the right
and the left valves equal Here we have inequail-
ties between the valves, and these Inequalities
are very great-Lot only are the two valves very
unequal, but you see the anterior edge car
red torward-the pOstcTiJr edge Is emargnate.
Now we have other bi.vaives. where one valve IS
very deep and the other fat but where the extre
mitudes are identical They are called the brachl-
opuds. Il is very important 10 ascertain these
facts, because they point to most extraordinary
! circumstance--t is this that IN shells i0und IN
strata. forming the crust Of our earth. we have
none which have the two valves unequal There
is not one bivave shell with eqdal valves IN any 81
the ancient strata There was not one 81 the an
cient hivalves which had this bia'erai symmetry
ia it's shells. Al belonged 20 that class where the
two sides could not yet be equal zed and stand np
right and Of course we must consider them as Oi n
lower grade than those where the sy mmetfy Is en-
tir,ly perfect
There is even something more. We have not
only the valves unequal, but the anterior and pos
terror extremities unequal Though these valves
are still unequal there is still an approach to ar
ference between the anterior and posterlor extrem
tiles The anterior extremity curves forward, though
the posterior does not yet extend backward But
the fact that there begins 10 be an equality shows
that these stand above those where the anterior
and pOsteror extremities are precisely Identical
Now again, those which are terrebrachela. which
have the anterior and posteror ends precisely den-
tical and the valves unequal are the Oldest. They
I'm the strata below the coal. and in the coal w e
have not yet any of those which have unequal
valves with unequal anterior and pOsteror ends
before we have passed the epoch OF the coal so
we see n graduation Of the animals IN each series
corresponding precisely with the order OF success
of understanding these facts which ut first appear
20 be rather insignificant Bot you ace when AZ.
femrted 10 show that there was difference IN the
actual position OF the animal in water how 1t stood
or law the law of succession oil types the
law of graduation OF organization from the earnest
appearance OF organic life up 10 the present time
Ofcourse the Oldest type once introduced have not
been allowed to die out. We have IN living state
several brachiOpgdR, but very few, perhaps one
fltieth OF the whole number, OF the acceptable w e
have OF these bivalves but they begin
about the middle age the history OF our earth aud
the number is about equal 10 the number OF types
now living. Now the symmetrical bivaves are the
most numerous living in our days, and those winch
occur only in the upper strata az the crust OF our
globe which begin in the last time, as 1t were, the
last historical and geological periods. OF course
there are some few species which run through a
greater range Of geological time. give only gen
era outline OF this succession IN order TO show the
importance of this thing.
Perhaps il would be more atiractivetO enter into
details Of the mode of living OF these animals their
uses habits and so forth; but these things may be
found 10 almost evtfy textbook, while anatomical
details and these more general bearings OF the struc
ture with geological phenomena. are scattered IN
isolated papers and some of these views have only
been known for short time. so that perhaps 1t IS
more advisable to stick to this point OF view rather
than what is usually called the history OF these
animals lApplausel 10 will OF course be per
ceyed that this difference between the biyaves is
less important than has generally been considered
Whether the mantle be united with the whole
length of the animal and whether il be opened oT
a greater portion is Of less importance than many
conchologists have thought.
And again. whether such an animal has hard
shell or not is of trifing importance. We have IN
fact. great number OF animals quite similar IN
their structure with the bvalve shells which have
no shells p, all-and have only membraneous GOV
ern. aud it is according TO this difference that the
class of acephem has been divided into the follow
ing groups;