Sissoa.] GASTROPODA. 203 



penultimate whorl, produced into small nodules at the points of inter- 

 section ; 3 distinct and smooth, spiral riblets upon the base. Colour 

 white or yellowish. Spire elevated conic, 2J times the height of the 

 aperture. Protoconch papillate, the nucleus slightly tilted, of 1| spirally 

 striate, strongly convex whorls. Whorls 7, regularly increasing, con- 

 vex, bicarinate at the periphery, shouldered above, flatly receding 

 below ; base flatly convex. Suture deep, lirate. Aperture oblique, 

 oval. Peristome continuous, thick, double. Columella oblique, arcuate. 

 Operculum unknown. 



Diameter, 1-5 mm. ; height, 3 mm. 



Animal unknown. 



Type in the Tasmanian Museum, Hobart. 



Hob. Stewart Island, in 18 fathoms (Captain Bollons) ; Foveaux 

 Strait ; Hauraki Gulf ; Cape Maria van Diemen ; near the Snares 

 and Bounty Islands, in 50 fathoms (Captain Bollons) ; Dusky Sound, 

 in 30 fathoms (R. Henry) ; Taumaki Island, South Island, in 10 fathoms 

 (Captain Bollons). The type is from Long Bay, Tasmania. Also re- 

 corded from Australia. 



Subsp. Lyalliana, Suter, 1898. 



Rissoa cheilostoma, T.-Woods, subsp. Lyalliana, Suter, P. Mai. S., iii, 6. 



Shell slightly shorter, less distinctly clathrate, the spiral riblets 

 being much more prominent, and the upper spiral riblet at a greater 

 distance from the suture. Colour cinereous or rufous, occasionally 

 yellowish- white, the base with a broad brown spiral band. 



Type in my collection. 



Hob. Lyall Bay, type (A. Hamilton) ; Titahi Bay (Miss Mestayer) ; 

 Foveaux Strait ; Hauraki Gulf (H. S.). 



7. Rissoa exserta, Suter, 1908. Plate 12, fig. 7. 

 Sissoa exserta, Suter, P. Mai. S., viii, 28, pi. 2, f. 22. 



Shell small, elongately ovate, imperforate, thin, semitransparent, 

 but faintly shining, strongly axially costate and spirally striate. 

 Sculpture consisting of distant, stout, axial riblets with a rather sharp 

 edge, 10 to 11 on the upper whorls, 12 to 14 on the body-whorl, on 

 which they vanish below the periphery ; the interstices and the riblets 

 are crossed by distant spiral threads, about 14 on the body- whorl ; 

 they are closer together upon the base. Colour white, the apex pinkish- 

 brown in fresh examples. Spire elevated conical, about twice the 

 height of the aperture ; outlines slightly convex. Protoconch small, 

 globular, of 1 J microscopically densely spirally striate whorls. Whorls 

 4, the last large in proportion, flattened below the suture, thence 

 strongly convex ; base rounded. Suture deep. Aperture subvertical, 

 oval. Peristome continuous, thickened inside, sharp. Outer lip with a 

 varix formed by the last axial riblet. Basal lip slightly effuse. Colu- 

 mella oblique, short, slightly arcuate. Operculum unknown. 



