MOLLTJSCA OP THE ' CHALLENGER ' EXPEDITION. 403 



but are convex below this point ; the base contracts rapidly, and 

 runs out into a longish narrow snout. Suture well marked and 

 a little constricted. Mouth club-shaped. Outer lip, convex and 

 in front direct, it retreats very slightly in its course from where 

 it leaves the body, forming a very small, shallow, and open rounded 

 sinus. Inner lip is slightly hollowed on the body ; straight on the 

 upper part of the pillar but early cut off it advances with a long- 

 drawn obliquity to the point of the shell. H. 32. B. 012. 

 Penultimate whorl, height 0-06. Mouth, height 015, breadth 

 005. 



I doubt whether the only specimen of this species is full-grown, 

 and the mouth is a little chipped ; but the lines of growth indi- 

 cate plainly enough the form of the lip. It may be classed with 

 the P. nivalis group. 



12. Pletjkotoma (Sukcula) ischna, n. sp. (laxvos, lean.) 

 St. 169. July 10, 1874. Lat. 37° 34' S., long. 179° 22' E. 

 N.E. from New Zealand. 700 fms. Grey ooze. Bottom tempe- 

 rature 40°. 



Shell. — High, narrow, conical, blunt, with a contracted base 

 and longish snout, little sculpture, strongish, yellowish grey, 

 porcellanous. Sculpture. Longitudinals — there are only strongish 

 regular lines of growth, which rise into small tubercles, espe- 

 cially on the upper whorls ; between the stronger lines the sur- 

 face of the shell is delicately fretted with other very minute 

 sharp lines. Spirals — the whorls are faintly keeled above the 

 middle by a spiral thread, which is a little stronger and more pro- 

 minent than any of the others. Close above the suture is another 

 almost as strong,and which also slightly carinates the whorls; half- 

 way between these is a finer thread, which tends to split into two 

 very fine threads ; at the suture, but visible beyond the mouth, is 

 another thread, which here defines the base. The longitudinals 

 rise into very small tubercles as they cross the spirals ; but this 

 feature is much strongest on the upper whorls, which are reticu- 

 lated ; on the last whorl it is feeble. Between the keel and the 

 suture lie three very fine, equally parted, threads. On the base 

 and snout are about twelve pretty equal fine threads. Colour 

 a faintly yellowish grey. Epidermis extremely thin, smooth. 

 Spire conical, with an almost unbroken profile, the whorls being 

 scarcely convex. Apex — there are barely two embryonic whorls, 

 smooth, globose, not flattened down at the tip, which, however, is 



