CONCHOLOaiCAL WRITINGS. 23 



4. Sub-genus. Shell transverse, thick, not truncated; knobby or 

 warty. 18. P. gibbosus ; 19. P. verrucosus; 20. P . tubercularis ; 

 21. P. nodosus. 



5. Sub-genus. Shell rounded or longitudinal. 22. P. pusillus ; 

 23. P. subrotundus ; 24. Potamilus obovalis. Raf. 



II. G. PiiEnROCERA. Univalve. Shell variable oboval or conical, 

 mouth diagonal crooked, rhomboidal, obtuse aud nearly reflexed at 

 the base, acute above the connection, lip and columelle flexuose 

 entire. Animal, with an operculum membranaceous, head separated 

 froni the mantle inserted above it, elongated, one tentaeulum on each 

 side at its base, subulate acute,, eyes lateral exterior at the base of 

 the tentacula. 6 species. 1. PI. retusa ; 2. PI. saxatilis ; 3. PI. 

 fasciata; 4. PI. coneola; 5. PI. angulata ; 6. PI. turricula, 

 Raf. 



III. G. Ambloxis. Univalve. Shell thick oboval, mouth oval, 

 rounded at the base, obtuse above with a thick appendage of the lip, 

 columelle flexuose, a small rugose ombilic. 2 Species, 1 A. eburnea ; 

 2. A. ventricosa. Raf. 



[From the American Monthly Magazine and Critical Eeview, Vol. IV, 



page 39, New York, 1818.] 

 Farther Account of Discoveries in Natural History, in the Wes- 

 tern States, by Gonstantine Samtiel Rafinesque, Esq., com- 

 municated in a Letter from that ffentleman to the Editor. 

 [42] 



8. N. G. Ellipstoma. (Univalve Shell. Nat. fam. Neritinia.) 

 Shell oval, obtusp, mouth oblique, elliptical entire, thick lips, the 

 inner one plaited, smooth covering the columella and ombilic, de- 

 current and notched outside the mouth, below the columella. Three 

 species. 



8. N. Sp. Ellipstoma gibbosa. 4 spires, a large knob behind the 

 outward lip. Prom the Ohio and Wabash, length half an inch. 



9 N. Sp. Ellipstoma zonalisa. 3 spires, smooth, 3 transverse, 

 zones violet. Kentucky river. 



10. N. Sp. Ellipstoma rugosa. 5 spires, smooth, sutures 



wrinkled. Ohio river., 

 [loe] 



General Account of the Discoveries made in the Zoology of the 

 Western States. By G. F. Rafmesque, in 1818. 



8. MoLLTTSCA. As many as 25 new genera, and 212 species, 

 (mostly new) have been discovered ; many of which, however, are 



