13 



PLANORBIS TRIVOLVIS, Say. 



Plate 2.— Figs. 4—7. 



P. testa utrinque excavata, ad sinistram subcarinata, 

 anfractibus 4 subcylindi-aceis: pagina dextra in medio 

 umbilicata. 



SYNONYMS AND REFERENCES. 



Lister. Conch, tab. 140, fig. 46. 



F. TRIVOLVIS, Say. Nich Encyc, art. Conchology, pi. 2, 

 fig. 2. — Am. Conchology, pi. 54, fig. 2. — Bulla fluviatilis, 

 (non Turt.,) Journ. Acad., ii. p. 31. (Junior.) 



P. coRPVLENTus, Say. Wiiittemore. Am. Journ. Sci., 

 vol. 38, p. 193, 



P. REGULARis, Lea. Proc. Am. p. S., vol. 2, p. 32. 



DESCRIPTION. 



Animal "dark russet or dusky, covered with 

 pale yellowish dots." — Gould. 



Shell flattened laterally, having four sub- 

 cylindrical whirls, which are finely striated 

 across by the lines of growth: left side slightly 

 carinated, the carina being most apparent upon 

 the inner whirls: spire slightly impressed, and 

 (within the last whirl) nearly level: there are 

 two and a half whirls visible upon the right 



