PTEROCYCLOS. 277 



instead of simple and horny, are from the Islands of the 

 Eastern Archipelago, principally from Borneo and Java. 



Species of Opisthopoirus. 



biciliatus, Mouss. tubuliferus, Pfeiff. 



rostellatus, Pfeiff. 



Genus PTEROCYCLOS, Benson. 



Operculum convex, elevated, multispiral, deeply concave 

 internally, composed of a calcareous spiral lamina covered 

 with a horny layer. 



Shell suh-discoidal, widely umbilicated ; aperture circular ; 

 peristome double, the external dilated superiorly into a wing 

 or tectiform beak, the internal short and incised on the right 

 margin. 



Syn. Steganostoma, Troschel, 



Ex. P. rupestris, Benson, pi. 85, fig. 3. Operculum, 

 P. rupestris, fig. 3, a, 3, b, 3, c. 



The species of this genus inhabit India and the Islands 

 of the East-Indian Archipelago, Ceylon, and Cochin-China. 

 The shells have the same tectiform canaliculate wing seen 

 in My.vostoma and Opisthoporus, but the structure of the 

 operculum will distinguish them. 



Species of Pterocyclos. 



Albersi, Pfeiff. nanus, Bens. 



auguliferus, Soul. parvus, Pears. 



bilabiatus, Bens. rupestris, Bens. 



Blandi, Bens. tenuilabiatus, Metcalfe. 



Cumingi, Pfeiff. Troscheli, Bens. 



VOL. II. O O 



