178 Panama Shells. LITTORINID^E. 



245. Rissoa fortis. Nov. sp. 



Shell long, ovate conic : white : with, on each whorl, about 

 twenty-two to twenty-four stout prominent approximate ribs, 

 which converge at the anterior extremity, where they become 

 very small : apex acute : spire with the outlines curvilinear : 

 whorls ten, slightly shouldered, moderately convex, with a well 

 impressed suture ; last whorl ventricose : aperture oblique, 

 ovate, retreating above, deeply effuse : labrum much advanced 

 in the lower half, very thick : labium thick : umbilicus want- 

 ing. 



Mean divergence about 33 ; length .29 inch ; breadth .12 

 inch ; length of spire .185 inch. 



This species resembles R. ambigua Gould, and is very different 

 from Rissoina Inca Orb. 



Station. Under stones near low water mark. 



Habitat Taboga ; C. B. A. ! 

 31 specimens were collected. 



246. Rissoa (I) incoiispicua. Nov. sp. 



Shell ovate conic : white : with several spiral ridges, of which 

 two or three are seen on the spire : with about twelve or four- 

 teen transverse narrow ridges, which are obsolete anteriorly : 

 apex subacute : spire with curvilinear outlines : whorls four, 

 very convex, with a deep suture : last whorl rather ventricose, 

 short : aperture orbicular, scarcely effuse : lip well thickened : 

 with a very minute umbilicus. Perhaps this species should 

 have been referred to CINGULA. 



Mean divergence about 55 ; length .045 inch : breadth .03 

 inch ; length of spire .032 inch. 



Station. Unknown. 



Habitat. Panama ; C. B. A. ! 

 1 specimen was obtained. 



