M '^ ^ k/^<. 



OF CONCHOLOGY. 47 



from the cardinal teeth ; posterior hinge plate broad and entire 

 in the left valve. e> 



It is probable that the Cretaceous A. sinuata, d'Orbi^i^ny, is a 

 species of this genus, as the external character is very similar. 



ASTARTE TELLINOIDES, Conrad. Eocene. 



A peculiarity of L. tellinoides is that the broad flat surface 

 of the posterior cardinal tooth is rugoso-striate transversely. 



This genus is a link between Crassatella and Astmie. 



RADIOCONCHA, Conrad. 

 Compressed, inequilateral, radiated ; hinge without a distinct 

 \ cardinal pit. /? // ' 



Crassatella GuERAsa-ERij d'Orbigny. ^ ^ ^ -,^ 



C. RoBiNALDiNA, d'Orbigny.-, - ; ./, , 



This genus, though nearly allied t6 Crassatella, ii sufficiently 

 distinct in hinge and sculpture. It existed only in the Cretaceous 

 period. 



PACHYTH^RUS, Conrad. 



This genus of fossil shells is closely allied to Crassatella. The 

 pit behind the cardinal tooth of the right valve is generally much 

 wider than in Crassatella, and there is a small pit behind the 

 posterior cardinal tooth of the left valve not seen in Crassatella, 

 while the inner margin of all the species is densely though finely 

 crenulated. This character marks every species down to the 

 Eocene, inclusive- In the Miocene species the margin is entire, 

 and generally so in the recent, although two or three have 

 subtuberculiform, much larger crenulations than any of the 

 fossils. This difference in character between the fossil and 

 recent species is very obvious, and in the Cretaceous species the 

 comparatively smaller cartilage pit and the large triangular pit 

 under it give the hinge a very different aspect from that of the 

 Miocene and recent species of Crassatella ; but in the elongated 

 Eocene forms this character is less obvious, and is nearly the 

 same as in the living genus Crassatella. Type, Crassatella 

 Vindiemensis, d' Orbigny.- 



According to the above generic character the genus Crassatella 

 originated in the Miocene Period. 



Crassatella pteropsis, Gabb, not Conrad. 



Mr. Gabb described this species in Part iv, 2d series of Journ. 

 Acad. Nat. Sc. by the same name as a species I described in the 

 same No. Both are from the Ripley Group, Mr. Gabb's species 

 from Tennessee and Alabama. I think Mr. Gabb's shell is the 

 young of pteropsis, Conrad. I found it at Haddonfield, of a 



