496 Desc?^ipliojis and Notices of 



P. Havanensis, Pfeif. P. Cubensis, Pfeif. P. cultratus, 

 D'Orb. P. Lanieriana, D'Orb. 



A fifth species is one of much interest ; inasmuch as its 

 throat is armed with teeth, very much Hke P. armigerus, Say. 

 The latter, Mr. Haldeman has proposed to consider as the 

 type of a new genus, (Discus). Should this claim be con- 

 firmed, another species may be added to the genus. It may 

 possibly be the species characterized by Pfeiffer under the 

 name of P. albicans,* but if so, he has failed to notice its most 

 interesting character, I therefore venture to propose for it the 

 name P. dentatus. 



Planorbis dentatus, Gould. Plate 24, fig. 14. 



Testa discoidea, soIidul&, pallide cornea, utroque umbilicata ; anfr. 3 leviter 

 striatis, supra et infra subcarinatis ; suturA profunda ; apertura sublunatS ; 

 labro intus callo albo incrassato ; fauce dentibus sex, abditis, armata. 



Shell discoidal, rather solid, pale horn-colored, about equal- 

 ly umbilicated on both sides ; whorls three or a little more, 

 feebly striated and slightly carinated above and below ; aper- 

 ture embracing about half the penultimate whorl, rounded lu- 

 nate, the lip supported within by a rib-like, white callus; at a 

 distance of about one fourth of a volution within the throat are 

 six unequal, lamellar teeth, two on the inner, one on the up- 

 per, and three on the outer aspect of the throat ; their place 

 may be readily seen through the shell ; diameter, ^^ inch ; 

 height, ^V inch. 



Found in a small lagoon at San Jorge. 



If there is any one portion of the globe which would reward 

 conchological research more than another, I believe it to be 

 the West India Islands. Notwithstanding they have been so 

 long known and so much frequented by all nations, a very 

 small portion of the species, it is believed, have been collected, 

 and those few have been poorly described and badly figured ; 

 so that it is not easy to determine them. One reason for the 



* p. orbiculari, utrinquc umbilicata, solidula, albicante vel pallide fulvicante; 

 anfr. 3 teretibus ; labro subincrassato, albo ; apertura subovata. 



