212 GASTROPODA. [Pectinibranchia. 



B. Shell without microscopic spiral sculpture. 



a. Spire nearly twice the height of the aperture ; shell 



subcylindrical, suture margined . . . . . . leptalea. 



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



oval, suture not margined . . . . . . micans. 



aaa. Spire of about the same height as the aperture, or but 



little higher. 

 b. Suture deep, subchunnelled. 



c. Shell of 4^ whorls, oval, height 2-3 mm. . . vulgaris. 



cc. Shell of 3 whorls, globular, minute, height 



1-25 mm. . . . . . . . . . . atomus. 



bb. Suture only impressed ; shell oval, rimate . . verecunda. 



20. Rissoa atomus, Suter, 1908. Plate 12, fig. 20. 

 Rissoa atomus, Suter, P. Mai. S., viii, 30, pi. 2, f. 27. 



Shell minute, globular, rimate, smooth, translucent, and polished. 

 The only sculpture consists of microscopic growth-lines. Colour light 

 yellow. Spire short, with a blunt apex, very little higher than the 

 aperture ; outlines convex. Protoconch small, depressed, flatly convex. 

 Whorls 3, convex, rapidly increasing, the last volution occupying 

 about four-fifths of the whole height ; base rounded. Suture deep, 

 sometimes deeply channelled on approaching the mouth. Aperture 

 rotundly ovate, angled above. Peristome continuous, very little cal- 

 lous, edge rather blunt. Columella subvertical, slightly arcuate. Inner 

 lip a little reflexed, and producing an umbilical chink. Operculum 

 unknown. 



Diameter, 1 mm. ; height, 1-25 mm. 



Animal unknown. 



Type in my collection. 



Hab. Bounty Islands, in 50 fathoms (Captain Bollons). 



Remarks. Nearly allied to R. micans, Webster, which, however, has 

 3-| to 4 whorls, and is much less globose ; specimens from Hauraki 

 Gulf measure 1-1 mm. bv 1-5 mm. 



21. Rissoa infecta, Suter, 1908. Plate 12, fig. 21. 

 Rissoa infecta, Suter, P. Mai. S., viii, 31, pi. 3, f. 31. 



Shell minute, oval, rimate, translucent, thin, polished. Sculpture : 

 A few faint spiral lines are sometimes present below the periphery 

 on the last whorl ; growth-lines very fine, oblique or nearly straight. 

 Colour light horny. Spire conical, a little higher than the aperture ; 

 outlines slightly convex. Protoconch small, globose, smooth. Whorls 4, 

 convex, the last large in proportion ; base rounded. Suture impressed, 

 narrowly margined below. Aperture slightly oblique, oval, angled 

 above. Peristome not continuous, not thickened, thin and sharp. 

 Columella vertical, nearly straight. Inner Up slightly expanded, and 

 forming a thin layer on the parietal wall. The umbilical chink is dis- 

 tinct. Operculum unknown. 



