PLANORBIS EXACUTUS. 21 



direction parallel with the axis; but from the 

 rarity of the shell in collections, overgrown spe- 

 cimens of P. trivolvis, (pi. 2, fig. 5,) have been 

 supposed to represent it; and it has accordingly 

 been referred to this species, or described as 

 resembling it very closely. 



PLANORBIS EXACUTUS, Say. 



Plate 4. — Figs. 1 — 3. 



P. testa lenticular!, parva, tenui, umbilicata; ad periphae- 

 riam carinata: anfractibus 4, supra planis, infra convexis: 

 apertura obliqua. 



SYNONYMS AND REFERENCES. 



P. EXACUOUS, Say. Journ. Acad. Nat. Sci., vol. 2, p. 166. 

 P. EXACUTUS, Gould. Invert, of Mass., p. 208, fig. 137. 



Lea. Tr. Am. Phil. Soc. 2d. 



P. LENS AND BRONGNIART, 

 P ALU DIN A HYALINA, 



s., vol. 6. p. 68, pi. 32, fig. 

 83. — Proceedings, vol. 2. 

 p. 242. 



DESCRIPTION. 



Animal reddish-brown, tentacles short and 

 slender, eyes black, foot short. 



