68 DENTALIUM-FISSIDENTALIUM. 



D. CERAs Watson. PI. 3, fig. 41. 



Shell like one of the old drinking-horns, stumpy, short, and a 

 good deal bent, rather thin ; the newer growth porcellanous, the 

 older chalky and given to break oif in flakes, leaving a perfectly 

 smooth, brilliant porcellanous core. Sculpture : The surface is 

 covered with close-set annular strite, which, especialh' on the longi- 

 tudinal ribs, show like minute, crisp, round threads. The longi- 

 tudinal ribs are very much stronger, but still are fine, rounded, 

 parted by rounded furrows much like the ribs ; both, but especially 

 the furrows, are irregular in size, fresh riblets arising in the hollows. 

 There are from 30 to 35 toward the apex, and from 70 to 80 toward 

 the mouth. Color, pure white. Edge thin and broken at the 

 mouth ; at the apex there is an irregular, ragged fissul-e in the con- 

 vex curve. Length 1*8, breadth at mouth 03, at apex 0'07 inch. 

 ( Watson). 



Animal, mantle is white, very thin and transparent ; the adductor 

 muscles are short and weak. The liver is small, of a light grayish- 

 brown. The mouth of the mantle is very strong, of a yellowish 

 color, and the animal is rather fawn-colored ( Watson). 



Mid-Pacific, east of Japan, 2050 fms. ; W. of Valparaiso; 2160 fms. 

 (Challenger). 



D. ceras Watson, Journ. Linn. Soc. Lond., xiv, p. 610 (1879). 

 Not D. ceras Dall, Bull. M. C. Z., ix, p. 37 (1881) ; Ibid., xviii, p. 

 425 (1889) ; Proc. U. S. Nat. Mus., xii, p. 294 (1890) ; Bull. U. S. 

 Nat. Mus., No. 37, p. 76 (1884).— D. keras Watson, Chall. Rep., p. 

 3, pi. 1, f.4(1885). 



" One specimen from mid-Pacific east of Japan is much less curved 

 than the others. That from W. of Valparaiso (distant more than 

 7,500 miles in a straight line, 4,500 miles north and south and 6,000 

 miles east and west) is much broader, length 1'7, breadth 0'36 inch, 

 and much more bent, but is obviously identical ( Watson). 



" The distance by sea from the Pacific, off Valparaiso, to the Gulf 

 of Mexico, is so enormous that Mr. Ball's identification of his spe- 

 cies with this one seemed to need confirmation, and a specimen was 

 accordingly sent to him for comparison. Mr. Dall sent me a sketch 

 of his solitary specimen with the following remarks, which his 

 sketch confirms: " Yours is older, has lost much tip, and widened at 

 the mouth ; the tip is, perhaps, slightly more curved. The sculpture 

 in mine, perfectly preserved, is a little more clearly cut than in yours. 



