226 GASTROPODA. [Pectiuibranchia. 



the aperture, outlines nearly straight. Protoconch minute, globular. 

 Whorls 5, regularly increasing, flatly convex ; base rounded. Suture 

 not deep. Aperture roundly ovate, slightly angled above. Peristome 

 continuous, faintly callous and whitish, sharp, very thin over the 

 parietal wall. Columella subvertical, arcuate, thickened but not re- 

 flexed. Operculum ovate, subspiral, with a long shelly process from 

 below the nucleus (Hutton, I.e., pi. 1, f. K, 4). 



Diameter, 1-5 mm. ; height, 2 mm. (type) : usually 2 mm. by 

 3 mm. 



Animal light brown, foot and tentacles white. Eostrum emargin- 

 ate at the extremity ; tentacles long, slender, smooth ; eyes large, on 

 swellings at the outer bases of the tentacles. Foot large, rounded in 

 front, and emarginate behind ; opercular lobe small, simple ; sole 

 with a median longitudinal groove. (Hutton, I.e., pi. 1, f. K, 2.) 



Dentition. The central tooth is as broad as long, and with 5 cusps. 

 The first lateral tooth has 5 denticles, the middle one larger than the 

 others ; the second lateral with 3 denticles, the inner one the smallest ; 

 the third lateral is narrow, abruptly bent and expanded near the 

 base, it has 3 minute denticles. (Hutton, I.e., pi. 1, f. 3.) 



Type in the Canterbury Museum, Christchurch. 



Hob. The type is from Lyttelton Harbour. Throughout New 

 Zealand, on seaweeds, mostly in rock-pools. 



Fossil in the Pliocene. 



Var. annulata, Hutton, 1884. 



Rissoina olivacea, var. annulata, Hutt., N.Z.J.S.. ii. 173; P.L.S. N.S.W., 

 ix, 940 ; Webster, T.N.Z.I., xxxvii, 27'J. 



Distinguished from the species by the narrow white band below 

 the suture. In all other characters it does not differ from the species. 



Diameter, 1-5 mm. ; height, 2 mm. 



Dentition the same as in the species. 



Type in the Canterbury Museum, Christchurch. 



Hob. Hauraki Gulf, together with the species ; Banks Peninsula 

 (Iredale). 



Var. lutea, Suter, 1908. 



Rissoina olivacea, Hutt., var. lutea, Suter, P. Mai. S., viii, 33. 



Distinguished from the species by its light horn-colour, and in 

 being a little more slender. 



Diameter, 1-4-1-5 mm. ; height, 2-5-2-7 mm. 



Dentition unknown. 



Type in my collection. 



Hab. Maloney's Reef, Hauraki Gulf, type (H. S.) ; Lyttelton 

 Harbour, on seaweeds (H. S.) ; Titahi Bay, Cook Strait (Miss 

 Mestayer). 



Remark. Mostly together with the species. 



