180 Panama Shells. LITTOBINID^. 



249. Rissoa notabilis. Kov. sp. 



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

 fourteen transverse very prominent ribs, which have concave 

 summits ; with four spiral keels, of which the upper two are 

 more distant and are seen on the spire on each side of the 

 suture ; the transverse ribs are smaller in the parts between the 

 second and third keels, and are obsolete below the third : apex 

 Bubobtuse, smooth and shining : spire with the outlines recti- 

 linear except near the apex : whorls six, abruptly shouldered, 

 planulate, with the suture subcanaliculate : aperture ovate: 

 umbilicus wanting. 



Mean divergence about 24° ; length .06 inch ; breadth .027 

 inch. 



Station. — Unknown, 



Halitat. — Panama; 0. B. A.I 

 1 specimen was found. 



250. Rissoa scalariformis. Nov. sp. 



Shell elongate, ovate conic : dingy white : with, on each 

 whorl, eleven stout prominent acute compressed ribs, which are 

 continuous on the successive whorls ; covered with microscopic 

 spiral striae, which ascend the sides of the ribs but are obsolete 

 on their summits : apex acute : spire with the outlines mode- 

 rately curved : whorls eight, convex, with a well impressed 

 suture : aperture obliquely ovate, effuse above and below : 

 labrum moderately thickened, weU exciirved and produced 

 along the middle. 



Mean divergence about 33°; length .13 inch; breadth .05 

 inch ; length of spire .08 inch. 



Station. — Unknown. 



Hahitat. — Panama ; C. B. A. I 

 1 specimen was found in sand. 



