DENTALIUM. 17 



orifice minute, a little channelled on the convex side but without a 

 slit. 



Length 50, greatest diam. 5, least 1 mill. 



Length 52, greatest diam. 5*3, least '8 mill. 



China, Sea (authors) ; Japan, Nagasaki, (figs. 17, 18), and Bay of 

 Jeddo, f. 16 (Lischke) ; Hakodate (Schrenck) ; Kii coast (Stearns) ; 

 Ceylon (Tennent). N. Australia at Cape York, Princess Charlotte 

 Bay, Katow, New Guinea, Darnley Island, Torres Strait (Chevert 

 Exped.). 



D. octangulatum DONOVAN, Nat. Hist. Brit. Shells, v, pi. 162 

 (1803) ; quoted " octangulum " by Turton. D. striatulum (in part) 

 TURTON, Conch. Diet. Brit. Is., p. 38 (1819). D. aprinum MAWE, 

 Linn. Syst. Conch., pi. 33, f. 1 (not of Linne). D. octogonum LAM., 

 An. s. Vert., v, p. 344 (1818). DESK, Mem. Soc. Hist. Nat. Paris, 

 ii, p. 352, pi. 16, f. 5, 6 (1825). DELESSERT, Rec. de Coq., pi. 1, f. 

 1 (1841). CHENU, Illustr. Conchyl., i, p. 5, pi. 1, f. 21-23. Sow- 

 ERBY, Thes. Conch., iii, p. 102, pi. 223, f. 9 (1860) ; and in Conch. 

 Icon., xviii, pi. 2, f. 12 (1872). REEVE, Conch. Syst., ii, pi. 36, f. 8. 

 LISCHKE, Jap. Meeres-Conchyl., ii, p. 103 ;. iii, p. 75, pi. 5, f. 1-3 

 (1874). DUNKER, Index Moll. Mar. Jap., p. 153. BRAZIER, Proc. 

 Linn. Soc. N. S. Wales, 1877, ii, p. 55. ? D. octagonum ANGAS, P. 

 Z. S., 1878, p. 868 (Henley Beach, South Australia). Not D. octa- 

 gonum Costa, Fauna Reg. Nap., Dent., p. 19, pi. 1, f. 6 (1850). 

 D. octohedra LEACH, ms. label in Jeffreys coll. 



Out of 32 specimens before us from Japan, 2 have nine equal and 

 equidistant ribs, and in another one rib is replaced by two contiguous 

 smaller ones. The young are much more curved than adults ; and 

 in the latter the larger half of the length is scarcely arcuate. The 

 number of ribs is practically the chief character separating this from 

 D. sexcostatum. 



In some specimens the primary ribs become much lower toward 

 the aperture, which, while still octagonal, has the angles rounded 

 off, not projecting as in the typical form. 



Donovan supposed the species to be British ; but there can be no 

 doubt whatever of the identity of his types with the Lamarckian D. 

 octogonum. After arriving at this conclusion we found that Des- 

 hayes, in his MS. card catalogue, had adopted the same view. 

 D. JAPONICUM Dunker. PL 2, fig. 19. 



Shell solid, white, becoming yellowish toward the apex, a little 

 arcuate ; having 7 or 8 thick ribs, and interstitial riblets ; trans- 

 2 



