MOLLUSCA OF THE * CHALLENGER ' EXPEDITION. 509 



curve a slit O'l in. long, but interrupted by two bridges of the 

 shell which have not been removed when the fissure was made. 



From St. 73 and St. 78 the specimens belong to the typical 

 form ; that from St. II., a remarkably large and fine specimen, 

 belongs to a variety, D. capillosiim, var. pmtcicostatum, "W"., with 

 only about 40 instead of 65 longitudinal riblets or threads, 

 which are very flat on their top, and are divided by furrows re- 

 markably broad and square in form. These differences strike one 

 very strongly at first ; but the transverse sculpture is identical, 

 and there are spots on the typical specimens which present an 

 exactly similar form of ribbing. 



From St. 24 the specimen is only a fragment, and that of a 

 young shell of very diflicult determination. Count Pourtales, 

 however, having already found this specimen in the Grulf of 

 Mexico, his authority relieves me from the responsibility of giving 

 the West Atlantic as a locality for the species ; so I content 

 myself with adding a mark of interrogation to the ' Challenger ' 

 specimen. 



2. DektalIUM ^GEUM, W. (a'iyeos.) 



St. 149 (8). Jan. 29, 1874. Off London Eiver, Kerguelen 



Islands. 110 fms. Mud. 1 specimen. 



Shell. — Long, conical, finely tapering, much and very equally 

 bent, though less, of course, as the shell grows larger, thin, pure 

 white, porcellanous, a little chalky towards the mouth, but 

 higher up brilliant. Sculpture. Longitudinal ridges 30 to 35, 

 unequal, rounded, above close, rather high, narrow, and parted 

 by furrows which equal the ribs, but lower down these ribs be- 

 come broader and flatter and the furrows widen, till towards the 

 mouth the surface becomes uniform, and the ridges are only in- 

 dicated by the faint striae of the furrows. Under a lens the 

 whole surface shows a faint longitudinally striated texture. On 

 the upper part of the shell the striae of growth are very faint ; 

 but they become rather strongly marked towards the mouth. 

 Towards the apex the outer layers for half an inch are stripped 

 off, and leave exposed the brilliant smooth core, presenting 

 many longitudinal facets corresponding with the ridges of the 

 outer layer. There is an irregular short fissure with broken 

 edges at the apex on the convex curve. L. 2'5 in. B. at 

 mouth 0-3, at apex 0033. 



Than D. capillosum, Jeffr., this is more conical, more curved, the 



