14 EOCENE MOLLUSCA. 
‘This, like most of the species in this restricted genus, is very variable, assuming a 
shape in some degree conformable with the place in which the individual has chosen to fix 
its abode; and although the generality of specimens have the upper valve convex, it 
occasionally happens that this valve is flat or even slightly concave outwardly ; the form is 
sometimes clongately ovate, while at others it is elevated, but when quite free and not 
distorted it is nearly orbicular, as may be seen by the specimen figured, which displays its 
natural shape. The same habits existed in this anima! as in species of the genus at the 
present day. One of Mr. Edwards’s specimens adhered to the back of a Pecten, the 
markings and rays of which it has assumed with great regularity (fig. 1, c). 
In the young state of this shell the striz are wholly invisible, and, indeed, in some 
of the larger specimens they are only to be detected by a powerful lens; it is so in those 
from Clarendon, and this I imagine is the condition of those specimens to which the names of 
A. levigata and A. orbiculata have been given, The muscle-marks in the upper valve are 
well displayed; the larger one, the muscle of the plug, is situated under the cartilage-pit, 
and is more than double the size of the adductor, and corresponds with the large foramen 
of the lower valve; the shape of this mark is modified by the shape of the shell; the upper pedal 
impression is close to the corner of the cartilage-pit, and I had imagined at one time 
that a difference in form existed between the specimens from Clarendon and those from 
Barton, but apparently this is not a permanent character, and these markings are all 
variable in outline. In the specimens from Grignon the same variableness in these muscle- 
marks may be observed; they assume, in a great degree, a shape much in accordance with 
the outward form of the shell. I am unable to detect a difference which might fairly be 
considered specific between any of the specimens, from the lowest to the uppermost of 
the older 'Tertiaries through which this Anomia extends. The umbo or beak of the shell 
is likewise an unstable character; in some specimens it is immediately on the margin, 
while in others it is at a little distance from it, aud Mr. Sowerby says (‘ Min. Conch.’, p. 32) 
that the shell, when old, is contracted towards the beak, but this condition is probably 
accidental, as it occurs only in some specimens. 
Barton specimens seldom exceed an inch in diameter, while those from Brackles- 
ham are double that size. I have seen only a few from Clarendon, and those were 
small. The shell is generally more or less tinged with a reddish-brown colour, particularly 
the Bracklesham specimens, and probably contained a good deal of animal matter. This 
species ought strictly to be called 4. anomialis. 
2. Anomra scaBrosa, S. Wood. ‘Tab. XI, fig. 5, a—c. 
Spec. Char. A. testa minutd, orbiculatd, compressd, tenui ; valvd superiore costulatad 
vel radiata, et valde imbricata, imbricibus magnis et regularibus ; valvd inferiore planulatd ; 
Soranine parvo. 
Shell small, orbicular, somewhat compressed, thin; upper valve costated or radiated, 
with large and elevated imbrications ; lower valve with a small opening. : 
