DENTALIUM. 5 



rather wide and rounded, generally wider than the intervals; the 

 concave side as a whole with stronger sculpture than the convex 

 side ; growth striae faint. Aperture slightly compressed laterally, 

 not oblique. Anal orifice shortly ovate, the narrower end toward 

 the convex side ; no slit or notch. 



Length 75, length of aperture 6, breadth 5*5 mill. ; diam. of apex 

 2 mill. ; height of arch from chord 13 mill. 



Island of Bohol, Philippines. 



With the color and general shape of D. aprinum, this species pre- 

 sents less prominent and many more longitudinal riblets, without 

 trace of the definite arrangement seen in that species. It is not es- 

 pecially related to aprinum except in being of a green color. The 

 aperture is noticeably compressed from side to side. The figures on 

 pi. 5 represent the sculpture at the apex and aperture, with an out- 

 line of the latter. 



GROUP OF D. OCTANGULATUM. 



White shells with 6 to 13 strong ribs at the apex, continuing to 

 the aperture or becoming obsolete, the intervals either smooth, with 

 several striae, or a median riblet. Apex small ; anal orifice simple, 

 without terminal " pipe," slit, or notch (with very few exceptions 

 where a short slit occurs). 



An Indo-Pacific, West American and West Indian group, with 

 shells somewhat like the group of D. entalis but not colored, and 

 without the notch, sheath or other apical peculiarities frequently 

 developed in that series. 



Some species possibly belonging to this group have been placed 

 in the group of D. disparile, q. v. 



So many of the species are unfigured and insufficiently described 

 that a satisfactory "key " to them cannot now be constructed. The 

 Australian forms particularly are but little known. In the absence 

 of something better, the following synopsis may be found of some 

 use. 



Key to Species. 



I. Hexagonal or six ribbed at and near the apex. 



a. No large intercalated riblets toward aperture. 



b. Intervals smooth, with several striae toward aper- 

 ture; length 55 mill., 12 to 14 times the diameter. 

 Oriental, hexagonum, p. 18. 



