XX11 GEOGRAPHIC DISTRIBUTION. 



Key to Japanese and Chinese Dentalium. 



a. Primary ribs 6-13, strong, angulating the aperture ; shell 

 white or pale. 



b. Ribs 6 (rarely 7), strong, intervals with some riblets 

 generally, length about 55 mill., 12-14 times the diam., 

 hexagonum (p. 18) ; sexcostatum, p. 19* 

 b'. Ribs 7-9, some interstitial riblets. 



G. Ribs 7-8 ; length 72 mill., 12 times the diameter, 



japonicum, p. 17. 



c'. Ribs 8-9 ; length 50 mill., 10 times the diameter, 



octangulatum, p. 16. 

 e". Ribs 8-9 ; length 30 mill., 8 times the diameter, 



yokohamense, p. 16. 



b". Ribs 11-13, strong and narrow ; an interstitial thread 

 or none ; a wide, shallow apical notch ; length 70 mill., 

 11-12 times the diam., bisexangulatum, p. 16. 



a'. 16 narrow riblets at apex, increasing to double that number, 

 and then vanishing, the large end smooth except for growth- 

 lines, length 80 mill., 11 times the diam., weinkauffii, p. 40. 

 a". 6-1 2 riblets at apex, increasing to about double that number. 

 b. 6, increasing to 12 ; shell acute, rapidly widening ; 

 length 18 mill., 8-9 times the diam., intercalatum, p. 23. 

 b'. 8 ribs, increasing in number toward aperture ; cancel- 

 lated with growth-striae ; length 25 J mill., about 8 times 

 the diam., cancellation, p. 30. 



b". 12 delicate sulci, increasing to 30 ; length 20 mill., 8 

 times the diam., porcatum, p. 15. 



a'". 30 sulci, vanishing toward aperture ; length 30 mill., 10 times 

 the diam., buccinulum, p 14. 



a"". Smooth, glossy, white ; longitudinally finely striate at apex, 

 becoming smooth, aciculum, p. 93. 



a'"". Riblets very numerous ; shell large and solid. 



b. About 40 subequal riblets becoming alternating toward 



apex, where there is a long slit ; length 90 mill., 8-9 



times the diam., vernedei, p. 80. 



b'. Many unequal riblets ; a series of 2 to 5 holes in place 



of the slit ; length 47 to 64 mill., about 82 times the 



diam., plurifissuratum, p. 82. 



b". Numerous unequal riblets ; tawny, irregularly banded 



with brown ; tube compressed ; length 62 to 72 mill., 



about 6 times the diam., hungerfordi, p. 84. 



