126 DENTALIUM-COMPRESSIDENS. 



Less compressed and much more arcuate than D. brevicornu, and 

 more distinctly striated circularly. It tapers more rapidly than D. 

 pressum and is less compressed. D. ophiodon and D. platyceras are 

 conspicuously slenderer. The longitudinal cords are variable in 

 prominence, sometimes hardly noticeable. When well developed 

 they are rather coarse, and of the same character as in D. pressum. 

 Type no. 107700 U. S. Nat. Mus. 



D. OPHIODON Dall. PL 7, fig. 13 ; pi. 22, figs. 61, 62. 



Shell considerably curved, thin, slowly tapering, strongly com- 

 pressed between the convex and concave sides. Grayish-white, some- 

 what glossy. Sculpture : faint, fine irregular longitudinal striae with 

 very superficial interstices, crossed by fine irregular growth striae and 

 wrinkles, which bend forward on the concave side. Aperture irreg- 

 ularly oval, oblique, the peristome less curved along the concave 

 side. Apex oval, anal orifice simple, unslit. 



Length 15'5, greatest diam. at aperture 1*75, least 1*5 mill. 



Length 12'5, greatest diam. at aperture 1*3, least I'l, diam. at 

 apex 0-27 mill. 



Barbados in 100 fms. (Hassler Exped.) ; Blake stations 19-21, in 

 220-310 fms ; 10 miles off Cuba, lat. 22 38 f 40", Ion. 82 28' in 

 780 fms. (Dr. Wm. H. Rush). 



D. ophiodon DALL, Bull. M. C. Z., ix, p. 427 (1881) ; Ibid.,xviii, 

 Blake Rep., p. 427, pi. 26, f. 9 (1889) ; Bull. U. S. Nat. Mus., no. 

 37, p. 76, pi. 26, f. 9. 



The tube increases less rapidly in width than in D. pressum, it is 

 decidedly more curved, and the longitudinal sculpture is finer and 

 fainter. Dall writes as follows : 



" About the same length as the last species (D. pressum), more 

 slender, more acute, more translucent, more curved, and without the 

 evanescent indications of longitudinal striation ; the compression 

 results in less tendency to angulation, and there is an evident tend- 

 ency, in adult specimens, for the diameter at the mouth to be some- 

 what less than at a short distance behind it, a very marked dis- 

 tinction as between the two. The shell is quite translucent, and very 

 thin ; there is very little variation between the specimens. 



" The flattening is most prominent a little way behind the mouth 

 in the adult, and is best seen in an adolescent specimen." 

 D. PLATYCERAS Sharp & Pilsbry, n. sp. PL 22, figs. 58, 59, 60. 



Shell small, slightly curved, strongly tapering, dull, glossy toward 

 the aperture, white. Sculpture of rather irregular and decidedly 



