8 THE VOYAGE OF H.M.S. CHALLENGER. 



Shell— Very long and narrow, very slightly bent, and that almost entirely above ; a 

 very little flattened on the concave curve, so as to be slightly trigonal ; white, opaquely 

 porcellanous, a little glossy, not thick but strong. Sculpture: Closely and regularly 

 girt round elliptically with scratch-like puckerings in the lines of growth, of which there 

 are about 55 in the rath, of an inch. Longitudinally striped with fine ribs, of which there 

 are from 17 to 20, sharp and well defined by still broader furrows toward the apex, but 

 down the shell these increase in number and steadily decrease in definiteness till they 

 only show as a feeble system of lines on the rounded surface. At the apex there is on 

 the convex curve a ragged irregular fissure about O'l in. long. L. 1'93 in. B. at mouth 

 0-13, at apex 0"02. 



As compared with Dcntalium semipolitum, Sow., this is a longer, straighter, more attenuated 

 shell, with stria; stronger, blunter, and more persistent. It is not unlike Dcntalium antillarum, 

 D'Orb., in texture and in size, but is much straighter and narrower, and the early ribs are much 

 finer and fewer. It is intermediate in form between Dcntalium erectum, G. B. Sow., and Dentalium 

 splendidum, Desh., a little stumpier and more curved than the first, and less so than the second ; it 

 is much more longitudinally ribbed and less polished than either. Than Dentalium lessoni, Desh., 

 it is much more attenuated, and never so strongly ribbed longitudinally. Than Dcntalium inversum, 

 Desh., it is more strongly and persistently striate longitudinally. 



The young shell is perplexingly like that of Dentalium entalis, var. orthrum, Wats., but is a 

 little straighter, broadens more slowly, and the ribs project more sharply. In maturer specimens 

 this species is obviously much more attenuated than the former. 



9. Dentalium acutissimum, Watson (PI. I. fig. 8). 



Dentalium acutissimum, Watson, Prelim. Report, pt. 2, Journ. Linn. Soc. Lond., vol. xiv. p. 514. 



Station 218. March 1, 1875. Lat. 2° 33' S., long. 144° 4' E. N. of Papua. 1070 

 fathoms. Blue mud. Bottom temperature, 36° - 4. 



Station 246. July 2, 1875. Lat. 36° 10' N., long. 178° 0' E. Mid-Pacific, E. of 

 Japan. 2050 fathoms. Globigerina ooze. Bottom temperature, 35° - l. 



Shell. — Long and much attenuated, rather straight, and very regularly curved, very 

 thin, brilliant, and glass}-. Sculpture : The surface is crossed by fine sharpish irregular 

 stripe, which run very elliptically round. In the young shell the surface is regularly and 

 finely scratched by a great number of close-set, regular, sharp, and extremely minute lines, 

 which very gradually become more and more faint, but are still traceable even in the full- 

 grown shell. The colour is pure white, transparent, and almost hyaline in the fresh 

 shell, but in the dead shell the interior (not, as usual, the exterior) layers of the shell 

 become opacpue and chalky. The edge is very thin and irregularly broken. At the apex 

 the end is abruptly broken off in one specimen, in the other there is an irregular fissure 

 with an internal lining process. In the specimen from Station 246, which is full-grown, 

 but very short, a large, thin, irregularly shaped process projects, which being obliquely 



