1855.] Chusan Shells. 127 



3. Haliotidce Spire evanescent, Planorbis. 



Aperture patulous. P. corneus, auct. 



P. indicusy Benson. J. A. S. 

 5. p. 743. 



P. corpulentus, Say. Append, 

 to Exped. to St. Peter's 

 Eiver. PI. 15. Fig 9. 



4. Naticidce ?* 



5. Turbinidce. Aperture rounded, Omalodiscus, Benson. 



not encroached (fSpirorbis, Swainson.) 

 upon by the pre- 

 vious whorl. 



O. marginatus, Spirorbis al- 

 ius, &c. 



Planorbis hemispheric a, Benson. 



Testa nitida, olivaceo-cornea, supra convexa, apice planulata, infra 

 excavata, umbilico coarctato ; peripheric obtusa, nullo modo carinata. 



Diam. 0.25 poll. 



This species, belonging to the circle of Helicorbis, is nearly relat- 

 ed to the Sylhet umbilicalis, but differs in colour, in its greater con- 

 vexity and narrower umbilicus. The periphery is rounded, not angu- 

 late ; the spire has no depression below the surface of any of the 

 whorls, while the underside is concave. I have another species of 

 the subgenus in which the umbilicus is as narrow as in Trochorbis t 

 none of the previous whorls being visible. It will form the passage 

 from Helicorbis to that sub-genus ; it is from the Indus at Sukker, 

 is very minute, and was accidentally sent to me, secured from injury 

 in the hardened mud which filled the aperture of a Paludina ben- 

 galensis, picked up with other well known shells of the provinces by 

 a friend, on the bank of that river. 



" P. hemisphoerula is found in the same localities as P. papyraceus, 

 on Char a, Lemna, &c. It is not numerous. " 



* Is this family a fair representative of the Cyprceida among the Zoophaga ? 



f This name having long been pre-occupied by a genus of Annelides, Swainson's 

 subgenus requh*es a change of designation. Swainson has also called a genus of the 

 Olivince " Scaphula" without, observing that in 1834, I applied the name to a flu- 

 viatile form among the Arcadce. Zoolog. Journ. vol. v. 



S 



