MOLLTTSCA OF THE ' CHALLENGER ' EXPEDITION. 475 



rounded tubercles, of which there are about 11 on the first ordi- 

 nary and 16 on the last whorl ; on the earlier whorls they are 

 feebly prolonged downwards as riblets, but become weaker on 

 the last whorls. The whole surface is closely scratched with 

 hair-like and somewhat irregular lines of growth. Spirals — an 

 exceedingly slight pad forms a faint inferior margination to the 

 suture : between this and the line of tubercles the profile is 

 oblique and straight, not concave : below the keel formed by the 

 tubercles are a few very faint and sparse spiral threads. Colour 

 pale flinty, whence the name. Spire conical, with interrupted 

 profile-lines. Apex consists of two glossy, tumid, rounded whorls 

 of nearly equal size, and with a very slight suture. Whorls 8 in 

 all, of slow and regular increase ; they are shouldered above and 

 almost cylindrical below the keel ; the last is small, contracts from 

 the keel, and has a short, conical, hardly tumid base prolonged into 

 a short small snout. Suture very slightly impressed, rather 

 oblique. Mouth small, narrow, pear-shaped, angulated above, and 

 drawn out into a short open canal in front. Outer lip steeply curved 

 above, a little flatly prolonged forward ; its edge, which retreats 

 at the canal, is prominently rounded in the middle, and forms 

 a high shoulder above, between which and the body is the rather 

 deep, narrow, rounded sinus. Inner lip : there is a thinnish glaze 

 on the body and pillar, whose union is very slightly concave ; at 

 that point occurs the generic fold, which is somewhat remote 

 within the mouth, and is a rather strong thread ; the front of the 

 pillar is rather oblique, sharpish, and twisted. H. 0*41. B. 015. 

 Penultimate whorl, height 0-06. Mouth, height O09, breadth 

 0-07. 



This species differs from the preceding (which it very much 

 resembles) in that the shell is smaller, the whorls more sharply 

 keeled (the carination, too, higher), the contraction of their lower 

 part less marked, the tubercles are rounder and tend less to be 

 drawn out into riblets, the form of the shell is narrower, and 

 the apex is much smaller. 



37* 



