48 Mr: Martin's Account of fome Species of 
namely, a cavity or notch under the beak of the larger valve fur- 
nifhed with two fmall lateral prominencies ;' and in the fmaller valve 
a projection that correfponds with the notch and hollows that re- 
ceive the prominencies juft mentioned. But of this a better judg- 
ment may be formed by comparing Tab. 4. fig. 1, the top of the 
under valve of an Anomia, known in the recent ftate, and alfo found 
in great quantities foffil, with fig. 2, a correét drawing of the fame 
part of a petrified fingle valve’ of the ftraight-hinged Hine In this 
laft the cavity 2 (forming when the valves are ‘united a triangular 
aperture between the beak and hinge), and the pointed proceffes 
4, b, may perhaps anfwer the purpofe of the notch a, and lateral 
prominencies b, 6, fig. 1, though greatly differing in fhape. That 
this is at leaft probable will appear, if we examine fig. 5, which 
reprefents the petrifaction, fig. 2, as commonly found, of folid lime- 
ftone, with the valves joined. Here it is evident a part of the ca- 
vity, with the procefles * 4, 4, of fig. 2, are covered by the upper 
valve, the hinge of which, as in the recent Anomia, 1 {uppofe to be 
indented into the bottom of the notch, and furnifhed on the infide 
with hollows anfwerable to the prominencies in the other valve, 
Before however the whole internal ftru¢ture of the foffil ftraight- 
hinged Anomia can be properly determined, it will be neceffary to 
examine a perfect, detached upper valve, which I have never yet 
been fortunate enough to meet with. 
Of the Perforation. 
Some authors, in their definition of an Axzomia, have conftituted 
the perforation as the leading or effential character of the genus, 
and have even confined it to a particular part of the fhell—the 
* In a fpecimen of a fingle valve which I have lately met with, thefe proceffes are not 
ftraight, as in fig. 2. their points being curved inward, towards the hollow of the valve, 
fo as to refemble hooks. 
beak 
