Rissoa.] GASTROPODA. 211 



body-whorl. Spire conical, higher than the aperture ; outlines very 

 slightly convex. Protoconch globose, small, of 2 convex smooth whorls. 

 Whorls 5| to 6i, rather rapidly increasing, flat, periphery subangled ; 

 base rounded. Suture not much impressed. Aperture slightly oblique, 

 oval, angled above. Peristome continuous, but slightly thickened, 

 sharp, very little expanded. Columella short, arcuate, callous. Oper- 

 culum colourless, and presenting a malleated appearance on the inner 

 surface (fig. 196). 



Diameter, 1 mm. ; height, 2-25 mm. The usual height is 2 mm. 



Dentition. Fig. 19a. 



Type in Mr. W. H. Webster's collection. 



Hob. Devonport, near Auckland, type (W. H. Webster) ; Hau- 

 raki Gulf (H. S.) ; Cook Strait ; Lyttelton, under stones between tide- 

 marks (H. S.) ; Taumaki Island, South Island, in 10 fathoms (Captain 

 Bollons). 



Fossil in the Pliocene. One specimen from Wanganui in my col- 

 lection. 



Var. minor, Suter, 1898. 



Rissoa annulata, Hutt., var. minor, Suter, P. Mai. S., iii, 3. 



Smaller than the species, polished, no lighter band below the 

 suture, but the last half- turn of the body- whorl light horn-colour ; 

 the whorls are slightly convex, and the suture more impressed. 



Diameter, 0-75 mm. ; height, 1-5 mm. 



Type in my collection. 



Hab. Foveaux Strait, type (A. Hamilton) ; Banks Peninsula (Ire- 

 dale). 



Subgen. 6. SETIA, H. and A. Adams, 1852. 

 Setia, H. & A. Ad., A.M.N.H., x, 1852, 358. Type : P. pulcherrima, Jeffreys. 



Shell thin, obovate, oblong or subconic, subumbilicated or im- 

 perforate ; whorls usually few, rounded and smooth ; spire short, 

 apex obtuse ; aperture suborbicular, narrowed above ; columella 

 somewhat straight ; outer lip thin, simple, acute. 



KEY TO SPECIES. 

 A. Shell with microscopic spiral sculpture. 



a. Spire about twice the height of the aperture ; shell minute, 



pupiform ; suture margined . . . . . . lubrica. 



aa. Spire about 1 times the height of the aperture. 



b. Whorls rounded, suture marginate, imperforate . . microstriata. 

 bb. Whorls faintly shouldered, suture not margined, 



rimate . . . . . . . . . . porceiiana. 



aaa. Spire but little higher than the aperture. 

 b. Spirals on base only, suture margined. 



c. Imperforate, 3 spiral striae around the umbilical 



tract, suture subchannelled . . . . neozdanica. 



cc. Distinctly rimate, more than 3 spiral striae on 



base, suture only impressed . . . . infecta. 



bb. Spirals on the whole of the body-whorl, suture not 



margined . . . . . . . . . . stewartiana. 



