CONCHOLOGIOAL WEITINGtS. 8T 



14 G. OsBicuLA (Cuvier, Lamark.) Shell orbicular, one valye flat 

 and one conical. 



15 G. Strophesia, Raf. Shell orbicular equilateral, beak curved 

 in the great valve. 



16 G. Diclipsifes Raf. Differs from last by hinge short and 

 straight ; no proeminent beak. 



17 G. Trunoulites, Raf. Subequital, valves convex, equilateral, 

 nearly equal, hinge short and truncate. 



' 18 G. Productus, (Sowerby,) Equilateral, winged, or rather 

 auriciilated, one valve convex, the other flat or convex, hinge 

 linear. 



19 G. Styriasis, Raf. Differ from last by great valve, with a pro- 

 jecting cruciform appendage on the beak. 



20 G. Goniclis, Raf. Shell longitudinal, great valve concave 

 inside, with a longitudinal" angle outside. 



21 G. Megarites, Raf. Shell longitudinal, equilateral suborbicular, 

 valves nearly equal, both convex with concentric ridges, binge like 

 a linear horizontal fissure. 



Most of the species belong to the following Genera. 



Obovitps — 6 sp. 



Gonotrema — 15 sp. 



Platilites — 13 sp. 



Shophomenes — 16 sp. 



•In a supplement of March 1821, I added 2 N. G. 



22 G. Amblotrema, Raf. Differs from Gonotrema by the opening 

 or perforation, being oval or oblong, and obtuse. 



23 G. Pleuranisis, Raf. Differ from Platilites by having the 

 shell inequilateral. 



The geological age of these shells appears the same as that of 

 the oldest fossils, Madreporites, Turbinolites, Encrinites, &c., being 

 found together and promiscuously in the same strata, or in diluvial 

 debris ; but the different genera and species are not found together, 

 sometimes they are wide apart, or very rare ; they are mostly 

 siliciGed. 



