NATURAL SCIENCES OF rHILADELPHIA. 211 



RissoiNA SCABA, Garr., pi. 2, fig. G. 



Shell elongate-oblong, solid, vitreous, shining, white ; spire 

 rather long, turreted, gradually tapering from the body whorl, 

 apex obtuse; whorls 8, flatly convex, the last short and rounded, 

 longitudinally ribbed; ribs small, rather close, compressed, slightly 

 oblique, crossed by numerous small transverse ridges, forming 

 granules at their points of intersection ; suture deeply excavated ; 

 base obliquely grooved and ridged ; aperture small, oval, oblique, 

 and the basal sinus large ; peristome very thick, margined with a 

 stout external varix ; columella oblique concave. 



Length 4 mill. 



Hah. Viti Isles. (Coll. Garrett.) 



We obtained a single example at the above location and one at 

 the Samoa Isles. 



RissoiNA cosTATOGRANOSA, Garr., pi. 2, fig-. 7. 



Shell small, elongate-oblong, solid, shining, ashy-white ; spire 

 long, gradually tapering from the body whorl, apex obtuse ; whorls 

 9, convex, the last one rounded, longitudinally granosely ribbed ; 

 ribs rather small, closely set, slightly oblique, flexuous on the last 

 whorl, and transversely grooved ; suture deeply impressed ; aper- 

 ture oblique, sub-ovate, two-sevenths the length of the shell ; peri- 

 stome thick, finely crenulate, somewhat dilated. 



Length 5 mill. 



Hah. Viti Isles. (Coll. Phil. Acad. Nat. Sciences.) 



Five specimens found under clumps of coral on reefs. It be- 

 longs to the same group with R. 'Gerithiopsis, Pse. 



RissoiNA GRACILIS, Garr., pi. 2, fig. 8. 



Shell small, elongate, slender, cylindrically tapering, rather 

 thick, somewhat shining, light-brown ; spire long, sub-acute ; 

 whorls 9, convex, last one short, rounded, longitudinally ribbed; 

 ribs rather large, closely set, as wide as their interstices, slightly 

 oblique, and flexuous on the last part of the body whorl ; suture 

 margined beneath; aperture small, sub-oval, nearly vertical; peri- 

 stome thick, sinuous above and beneath ; columella concave and 

 callous. 



Length 3 mill. 



Hah. Yiti Isles. (Coll. Garrett.) 



A beautiful slender species belonging to the group of which 

 Rissoina ambigua, Gl., may be considered as the type. B. gra- 

 cilis also occurs at the Society Isles. 



