113 



pressed microscopic spiral stria? : apex acute: spire with slightly 

 convex outlines, often with a curved axis : whorls seven and one- 

 half, quite convex, with a well impressed suture : aperture mode- 

 rately effuse and rather large : labrum well produced and excurved> 

 rather thick. The name of this species was originally suggested by 

 specimens, in which the axis is more than usually distorted. Since 

 it has been used in other collections, and in my printed catalogue of 

 North American shells, I have not deemed it expedient to substitute 

 a more appropriate name. 



Mean divergence about 35°; length of spire .13 inch; total 

 length .21 inch ; breadth .095 inch. 



RissoA ABERRANS. Shell long ovate conic : white : strongly 

 sculptured with three or four spiral ridges, which are decussated, 

 with nodulous intersections, by transverse ridges, of which there are 

 about sixteen on each whorl ; anteriorly the transverse ridges are ob- 

 solete, and three or four additional spiral ridges are nodiferons : apex 

 acute : spire with the right side nearly rectilinear and the left quite 

 curvilinear, the axis being curved : whorls seven, nearly planulate, 

 with a subcanaliculate suture; last whorl rather large: aperture 

 rather small, deeply notched anteriorly; labrum rather thick and 

 well excurved. This species connects the genus with those Ceri- 

 thia, in which the canal is reduced to a notch. 



Mean divergence about 32°; length of spire .1 inch; total length 

 .165 inch ; breadth .08 inch. 



RisosA scALAROiDEs. Shell long ovate conic : white : with, on 

 each whorl, sixteen or eighteen stout ribs, which are continued to 

 the anterior extremity : apex acute : spire with the outlines mode- 

 rately curvilinear ; whorls seven and one-half, slightly convex, with 

 a well impressed suture : aperture moderately effuse : labrum well 

 advanced and excurved, rather thick. 



Mean divergence about 27°; length of spire .13 inch; total 

 length .2 inch; breadth .08 inch. 



Variety (?) minor is but .15 inch long. 



R. scalar elln Ad. (Proc. Bost. Soc. Nat. Hist., Jan. I, 1845,) 

 closely resembles the preceding ; it has on each whorl twelve to four- 

 teen ribs, which are larger than in R. scalaroides, and has, in large 

 specimens, the following dimensions : — Mean divergence about 24° ; 

 length of spire .1 inch ; total length .155 inch; breadth .00 inch. 



