128 



MOLLUSCA. 



No 365. Rhynchonella dentata, Hall. 



Cincinnati Group, Richmond, lud. 



No. 366. Rhynchonella capax, Con. 

 (Rhj'uchonella increbescens, Hall). 



This genus begins in the Lower Silurian; 500 species 

 are found fossil, and only six living. These specimens 

 are from the Cincinnati Group, Waj'nesville, Ohio. 



No. 367. Rhynchonella pleurodon, Phil. 



Carboniferous, Longuiddry, near Edinburgh, ScotJand. 



No. 368. [737, Cast]. Rhynchonella speciosa, Munst. 



From the Middle Oolite, Kelheira, Bavaria. 



No, 369. Rhychonella varians, d'Orb. 

 Oolite, Voegisheim, Baden. 



No. 370. Pentamerus oblongus, Sow. 



This fossil has a verj' wide distribution across the Silurian 

 basin of the New York system, where it serves to mark and 

 name a constant horizon — that of the "Lower Pentamerus 

 limestone." The genus is represented by 52 species in the 

 Devonian and Upper Silurian. From the Niagara Group 

 (Upper Silurian), Yellow Springs, Ohio. 



No. 371. Pentamerus oblongus, Sow. 

 Clinton Group, Rochester, N. Y. 



FAMILY ATRYPID^, 



Shell fibrous; beak curved; hinge-margin curved, with strong teeth; no 

 area; dorsal valve with spiral lamellae directed toward opposite valve. Very 

 similar to Rhynchonellidae. 



No. 372. Atrypa aspera, Schloth. 



Shell impunctuate, oval, usually plaited; dorsal 

 valve gibbous; beak small, often incurved and 

 concealing the round foramen. Occurs from 

 Lower Silurian to Trias, 21 species. Devonian, 

 Gerolstein, Prussia. 



No. 373. Atrypa primipilaris, d'Orb. 

 Devonian, Gerolstein, Prussia. 



