PEA RSOMA. ■RIIIOSTOMA. 127 



178. Pearsonia fairbanki, Blanford. 



Spirdcuhim fairhcaiki, JManford, J. A. S. B. xxxviii, 1869, p. 135; 



Pfeiffer, Mon. Pneum. Siippl. 3, 1875, p. 48 ; Theobald, Cat. 



Shells Brit. India, 1876, p. 38. 

 Pteroci/clos {Spiraculitm) fairhanki, Ilanley & Theobald, Concb. 



Ind". 1870, pi. 49, figs. \, 2. 

 Pterocyclus {Spiraculum) fairbanki, Nftvill, Hand List, i, 1878, p. 264. 

 Spiraculum {Diploptcrum) fairbanki, Kobelt & Miillendorff, Nachr. 



Dents. Maliik. Ges. xxix, 1897, p. 114; id., Cat. Pneum. 1899, 



p. 20. 

 Pearsonia (Pseudospiraculum) fairbanki, Kobelt, Das Tierreich, 



Lief. 16, 1902, p. 175, %. 37; id., Couch.-Cab., Cvclophoridae, 



ii, 1911, p. 770. 



Original descrijUion : — " Shell broadly uiubilicated, depressed, 

 nearly diseoidal, greyish white with irregular streaks and spots 

 of chestnut and two bands of the same colour; one, somewhat 

 interrupted, below the periphery, the other broader, within the 

 umbilicus. Spire almost flat, the apex prominent and papillar, 

 the suture dee|)ly impressed. Wliorls 5, rounded, the last cvlin- 

 drical, gradually descending in front and furnished, 4 mill, beliind 

 the aperture, with a short, nearly vertical spiracle, in the form of 

 a truncated cone, and joined to tlie penultimate whorl. Aper- 

 ture diagonal, circular, the peristome double, the internal portion 

 projecting slightly and obtuse, with a rather shallow angular 

 sinus near the suture: the external peristome is continuous, 

 expanded, dilated above into a projecting wing which runs 

 forwards for some distance along the last whorl in front of the 

 aperture, and is bent downwards at the end. Near the base of 

 the columellar margin there is a small gutter-shaped projection. 

 The operculum is very concave within, externallv convex, 

 flattened at the apex, with free lamellar edges to the whorls as in 

 the typical species of Pteroqjclos. 



"Major diameter 141, minor 11^, axis 0, diameter of the 

 aperture within 4 mill." (Blanford.) 



Hab. India : Pulney Hills (Fcnrbank). 



Genus RHIOSTOMA. Benson. 



Mhiostotna (part.), Benson, A. M. N. II. ser. 3, v, 1860, p. 9G; PfeilTer, 

 Jouru.Conchyl. x, 1862, p. 45; Blanford, A. M. N. H. ser. 3, xiii, 

 1864, p. 451 ; Pfeitler, Mon. Pneum. Suppl. 2, 1865, p. 38 ; Martens, 

 Pieuss. Exped. ()st-Asien,Zool.ii,1867,p. 63; Stolizckza,.T.A.S.B. 

 xl, 1870, p. 150 (animal); Nevill, Hand List, i, 1878, p. 262 (as 

 subgenus of Pterocyclus) ; Fischer, Man. Conchyl. 1885, p. 745 

 (subgenus); Kobelt & Miillendorff, Nachr. Deuts. Malak. Ges. 

 xxix, 1897, p. 115; id.. Cat. Pneum. 1899, p. 27; Kobelt, Das 

 Tierreich, Lief. 16, 1902, p. 170; id., Conch.-Cab., Cyclophoridae, 

 ii, 1910, p. 754. 



Type, Rhiostoma Jiaughtoni, Benson. 

 Ranr/e. Burma, Farther India. 



