264 RISELLA. 



R. INFRACOSTATA, Issel. PI. 50, figs. 41, 42. 



Narrowly umbilicated, minutely radiately striate above, concen- 

 trically, distantly costulate below; whorls somewhat convex, the 

 last with peripheral carina ; yellowish, maculated with brown at the 

 suture and periphery. Diam. 2 mill. 



Suez. 



R. Sismondi, Issel, Mss., is a synonym. 



Possibly only a variety of the preceding species. 

 R. RoEPSTORFFiANA, Nevill. PI. 50, fig. 43. 



Narrowly perforate, nearly smooth above, suture not subimbri- 

 cated, periphery rarely undulately waved; yellowish, sometimes 

 with a dark basal zone. Diam. 3"75 mill. 



Andaman Is., Mergui, Hong Kong. 



R. Templiana, Nevill., and vars. nigrofasciata and subimbri- 

 CATA, Nevill. (unfigured.) Andaman Is. 



Subgenus Plesiotrochus, Fischer, 1878. 



R. SouvERBiANUs, Fischer. PI. 50, figs. 44-46. 



Perforate, spirally striate, rather indistinctly longitudinally rib- 

 bed, ribs low and wide, rounded, undulating the peripheral carina ; 

 aperture produced below into a short, narrow canal ; yellowish 

 white, with thread-like spiral purj)lish lines interrupted by the ribs 

 and generally arranged in pairs, a purple articulated line at the 

 suture and periphery, another on the base. Length, 7 mill. 



Lifou, Loyalty Is. 



Subgenus Limnotrochus, E. A. Smith, 1880. 



R. THOMSON!, E. A. Smith. PI. 50, figs. 47, 48. 



Narrowly umbilicated, moderately solid ; whorls 7, flattened, with 

 a broad, deep furrow at the lower part, margined above by a keel, 

 which is nodulous on the lower whorls, above this there are three 

 granular spiral ridges, base with about eight ridges, and intervening 

 finer concentric strire ; basal margin of a])erture broadly sinuated, 

 excurved and slightly efflise; livid purplish, dotted with brown, 

 whitish at the suture and base. Length, 18 mill. 



Lake Tanganyika, Africa (fresh water.) 



R. KiRKi, E. A. Smith. PI. 50, figs. 49, 50. 



Narrowly umbilicated, dirty white ; wliorls 6 or 7, slightly con- 

 cave, with arcuate, fiexuous growth-lines, and 6 or 7 granular spiral 



