16 DENTALIUM. 



47, length of aperture 5, breadth 4-7 mill. ; height of arch from 

 chord 9 mill. The apical third is much more curved than in the 

 typical form, but this, like the greater ratio of diameter to length, is 

 a character of immaturity. 



D. YOKOHAMENSE Watson. PI. 2, figs. 29, 30, 31. 



Shell much curved when young becoming nearly straight with 

 later growth, little conical, rather strong, opaque, yellowish-white, 

 quite dull, but not chalky. Sculpture : Irregular, slightly elliptical, 

 lines of growth, a little puckered, generally slight, but sometimes 

 sharp and even ; towards the mouth faintly imbricated ; occasion- 

 ally marked by a deep furrow-like construction of the shell. The 

 longitudinal ribs are eight to nine in number, equal, rounded, rather 

 stronq, but not very prominent. These are parted by furrows, round 

 and open, very shallow, and of very unequal breadth. In these 

 furrows, one, two, or even three thread-like riblets appear, and in the 

 whole texture the lens shows a tendency to a longitudinal or rod 

 like structure. At the apex the shell is squarely truncate, and in 

 the young shell there is, on the convex slope, a slight ragged fis- 

 sure. Length 1*2, breadth at mouth 0'15 ; at apex 0'003 inch. 

 [Length 30, diam. 375 mill.]. ( Watson). 



Yokohama, Japan, 8 fms. (Challenger). 



D. yolcohamense Wats., Journ. Linn. Soc. Lond., xiv, p. 517 

 (1879) ; Chall. Rep., p. 11, pi. 2, f. 1. 



The ribs here are much less sharp than they are in DentaUum 

 dentalis Linn., and there is no trace of the exquisite longitudinal 

 fretted striae which cover the furrows in that species. The sharp 

 intercostal strise oi DentaUum octogonum are quite absent here; and 

 in that species, which is much more bent, the ribs are much wider 

 apart and more equally parted. ( Wats.). 



T>. ocTANGULATUM Donovan. PI. 2, figs. 16, 17, 18, 22. 



Shell rather slender, the length about 10 times the greatest diam- 

 eter, well curved, white or bluish-white; nearly lusterless or shining. 

 Sculpture, 8 (rarely 9) longitudinal rounded ribs, extremely strong 

 and prominent toward the smaller end, often lower toward the ajDer- 

 ture, parted by deep concave intervals, smooth in the young, but 

 usually with several or many unequal longitudinal strise in adult 

 specimens at least toward the larger end ; growth-lines slight. Aper- 

 ture somewhat oblique, octagonal, a trifle longer than wide. Anal 



