16 Mr. W. H. Benson on the Genus Opisthoporus. 



bulum as a true Ct/clotus, Guild., or with Taylorianus, &c. as an 

 Opisthoporus or a Coelopoma. 



In respect to Pteroci/clos (Lituus) brevis, Martyn, I am dis- 

 posed to associate it with Cijclophorus rather than with Ptero- 

 cyclos. The wing is not truly Pterocycliform, and is rather an 

 exaggerated representation of the angle and sulcus observed in 

 C. Nilagiricus and other Cyclophori ; while the thickened, horn 3^, 

 multispiral, and slightly concave operculum is closely related to 

 the same form. The internal face of the operculum has not 

 been yet described. It is smooth, the margin encircled with a 

 thickened, slightly elevated band ; and the centre is occupied by 

 a broad convexity, with a more prominent central reddish trans- 

 lucent boss, — a feature observable in C. Perdix and its allies. 

 The thimble-shaped operculum of Pterocyclos, horny or cartila- 

 ginous, with a calcareous skeleton or foundation, perforated in 

 the centre when denuded of its outer coating, can scarcely be 

 said to have any affinity with it. 



Of another shell, Pt. incomptus, Sow., classed by Pfeiffer with 

 Pterocyclos, I can say little. Its operculum is not known. The 

 prediction may however be ventured, that, when examined, it 

 will be found that the form will have no locus standi in Ptero- 

 cyclos. The wing here indicates an analogy, not an affinity to 

 the genus, and it may be expected that its operculum will be so 

 constituted as to associate it with such species as Cyclotus gigan- 

 teus and Inca. 



As every notice regarding the unrecorded opercula of the 

 Cyclostomacea tends to establish our knowledge of the family, 

 the following descriptions, in addition to those given in a recent 

 paper^ will not be without their use. 



Cyclotus semistriatus, Sow. 



Operculo caleareo, arete 6-spirato, nucleo planato ; margine anfrac- 

 tuum 4-5 exteriorum acute elevate, subreflexo, interstitiis concavis 

 profundis, scabre obhque plicatis. 



From specimens taken alive at Kirkee in the Deccan. 



' Cyclotus filocinctus J Bens. 



Operculo extus eoncavo ; anfractibus paucis, margine scabre elevato. 



Cyclophorus cuspidatus, Bens. 



Operculo tenui eoncavo, corneo, arctissime spirato, margine anfrac- 

 tuum linear i. 



Cyclophorus Indicus, Desh. 



Operculo crassiusculo, obscure rubello-corneo, 6-spirato, extus scabro, 



