GEOGRAPHIC DISTRIBUTION. XXI 



Key to Californian species of Dentalium. 



a. Shell longitudinally strongly ribbed. 



b. Ribs typically 6, decreasing anteriorly, 



neohexagonum, p. 19. 



b f . Ribs 12-20 at apex, 25-48 at aperture, agassizi, p. 26. 

 a'. Shell longitudinally striate near apex (or in young specimens, 

 throughout). 



b. Thin, closely, finely and evenly engraved toward apex, 



smooth and polished toward aperture; length 25-30 



mill., semipolitum, p. 91. 



b' ' . Rather solid and opaque ; larger ; unequally lirulate 



toward apex, pretiosum var. indianorum, p. 45. 



a". No longitudinal sculpture. 



b. Strong and solid, young striated, pretiosum, p. 44. 



b'. Quite thin ; deep water species ; no apical notch. 



c. Slender, with very slight curvature, and slow in- 

 crease. 



d. Very slightly curved, very slender ; length 

 30 mill., 16-19 times the diam., 



watsoni, p. 113. 



d'. Almost straight, very glossy ; length 30- 

 40 mill., 12-15J times the diam., 



rectius, p. 113. 



d". Curvature regular but slight ; length 45 to 

 69 mill., 11 to 14 times the diam., 



dalli, p. 114. 



c'. Short, decidedly curved, very rapidly tapering; 

 tube vertically compressed ; length 8*6 mill., 4 

 times the greatest diam., stearnsii, p. 253. 



Japan and China. 



Fifteen species of Dentalium, none of them deep water forms, are 

 known from this side of the Pacific from Hong Kong northward. 

 Five of these are more or less widely distributed in the East Indies 

 and Indian Ocean, the others being until now known only from 

 Japan and China. The dominant group is that of D. octangulatum. 

 There is one Antalis and three Fissidentalium. Dredging in deeper 

 water will doubtless reveal a rich fauna. 



One nameless Siphonodentalium (p. 141) is recorded from Corea, 

 and Cadulus clavatus (p. 185) occurs in Hong Kong harbor. 



