8 DENTALIUM. 



VI. Twelve to fourteen ribs at apex, increasing to about double that 

 many at aperture. 



a. 12 delicate longitudinal riblets increasing to 20 ; length 

 20 mill., 8 times the diarn., porcatum, p. 15. 



a'. 14 narrow ribs, increasing to 28 equal ones at aperture ; 

 length 16 mill., about 7 times the diam., 



buceinulum, p. 14. 



D. LESSONI Deshayes. PI. 6, figs. 86, 90. 



Shell rather straight, cylindrical, whitish-gray, with 8 to 10 ribs, 

 ribs obtuse, depressed, disappearing at the aperture. 



Allied to D. novemcostatum, but distinguished by form, curvature, 

 and disposition of the ribs. It is narrower, longer, less curved, con- 

 stantly of a yellowish-white uniform color, without transverse zones. 

 The ribs, numbering 8, 9 or 10, are contiguous at their bases, mod- 

 erately raised and rounded. They are more elevated toward the 

 apex, diminishing gradually and disappearing toward the aperture. 

 They are interrupted by some growth lines. The aperture is small 

 relative to the length of the shell. 



Length 50, diam. 4 mill. (Desk.). 



New Guinea (Lesson). 



D. lessoni DESK., Mem. Soc. Hist. Nat. Paris, ii, p. 357, pi. 16, f. 

 13 (1825). CHENU, Illustr. Conchyl., i, Dent., p. 5, pi. 4, f. 4 (not 

 4a). Not D. lessonii Sowerby, 1860, 1872. 



Lesson brought a necklace of four strings, composed entirely of 

 this species, from New Guinea, presumably procuring it from the 

 natives. The Mediterranean shells identified in the Thes. Conch- 

 and Conch. Icon, as D. lessoni are D. panormum Chenu. Whether 

 D. lessoni of Sowerby's " Marine Shells of South Africa," p. 48, is 

 the true lessoni, or some allied species, we do not know ; but it is 

 more likely D. strigatum Gld. 



D. DECEMCOSTATUM Brazier. 



Shell tapering, thin, white, slightly arched, longitudinally 10- 

 ribbed, ribs somewhat sharp, interstices nearly flat, transversely 

 finely striated, apex with a small perforation ; basal aperture large, 

 circular. Length 10 lines, diam. of apex i, diam. of base 1 lines 

 (Brazier). 



Katow, New Guinea, 8 fathoms, sandy mud (Chevert Exped.). 



D. decemcostatum BRAZ., Proc. Linn. Soc. N. S. Wales, ii, p. 55 

 (1877). 



