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



hulum as a true Cijclotus, Guild., or with Tciijlorianus, &c. as an 

 Opisthoporus or a Coelopoma. 



In respect to Pteroojclos (Lituiis) brevis, IMartyn, I am dis- 

 posed to associate it with Cijclnphorus 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 Cyclophoi^i ; while the thickened, horny, 

 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. incomj)tvs, Sow., classed by Pfeiffer with 

 Pteroci/clos, 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 gig an- 

 iens 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 calcareo, arete G-spirato, nucleo planato ; margine anfrac- 

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

 profundis, scabre oblique plicatis. 



From specimens taken alive at Kirkee in the Deccan. 



Cyclotus filocinctus, Bens. 

 Operculo extus concave ; anfractibus paucis, margine scabre elevato. 



Cyclophorus cuspidatus, Bens. 



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

 tuum linear! . 



Cyclophorus Indicus, Desh, 



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



I 



