116 



Mean divergence about 26^; length of spire .14 inch ; total length 

 .2 inch ; breadth .09 inch. 



RissoA sTRiosA. Shell ovate conic, somewhat turrited : dingy 

 white or corneous : with, on each whorl, twenty-five to twenty-eight 

 moderately developed transverse folds, which are obsolete on the 

 lower part of the middle whorls and on most of the last whorls ; with 

 very numerous crowded deeply impressed spiral striae ; with an in- 

 frasutural impressed line larger than the striae and constricting the 

 whorls : apex acute : spire with the outlines moderately curvilinear : 

 whorls nine, rather convex, with a moderately impressed suture : 

 aperture somewhat effuse, large : labrum well advanced, much ex- 

 curved, moderately thickened. 



Mean divergence about 26°; length of spire .135 inch; total 

 length .2 inch ; breadth .08 inch. 



RissoA pRiNCEPs. Shell ovate conic, turrited : white : with very 

 numerous crowded slender ribs, which become obsolete on the last 

 whorl, and strong crowded spiral striae, which become larger on the 

 last whorl : apex acute : spire with rectilinear outlines : whorls ten, 

 nearly planulate, slightly contracted next below the suture, which is 

 moderately impressed : aperture very effuse : labrum very much ad- 

 vanced a little below the middle, well excurved, moderately thick- 

 ened. This species resembles R. albida Ad., but that shell is much 

 smaller, and the outlines of its spire are curvilinear. 



Mean divergence about 30° ; length of spire .25 inch ; total length 

 .37 inch ; breadth .14 inch. 



RissoA (?) MELANURA. Shell couic, turrited : white, subtranspa- 

 rent, with the apex black : nearly smooth, shining, with some spiral 

 striae, which are quite distinct anteriorly and at the lower part of the 

 whorls of the spire, and are obsolete on the upper part of the whorls : 

 apex acute : spire with the outlines nearly rectilinear : whorls eight, 

 quite convex, with the suture rather deep : aperture scarcely effuse : 

 labrum thin (?), well excurved below the middle : columella straight, 

 subtruncate. On account of the imperfect condition of the labrum 

 in the specimens before me, it remains doubtful, whether this shell 

 is a Rissoa ; it is evidently kindred to R. tervaricosa Ad., whose 

 generic character is also doubtful, the labrum being thickened by 

 the last varix. 



Mean divergence about 2S° ; length of spire .21 inch; total 

 length .28 inch ; breadth .11 inch. 



