14 KOGKNi: MOLLUSC A. 



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 elongately 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 animal 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 stripe 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. laevigata 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, and 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 A. anomialis. 



2. Anomia scabrosa, 8. Wood. Tab. XI, fig. 5, a — c. 



Spec Char. A. testa minutd, orbiculata, compressd, tenui ; valvd superiorc costulatd 

 vet radiatd, et valde imbrkatd, imbricibus magnis et regularibus ; valvd inferiore planidatd ; 

 f or amine par oo. 



Shell small, orbicular, somewhat compressed, thin ; upper valve costated or radiated, 

 with large and elevated imbrications ; lower valve with a small opening. 



