74 DENTALIUM-FISSIDENTALIUM. 



towards the front margin ; these stride are crossed by extremely 

 numerous and close-set circular microscopic lines. Color, glistening 

 white. Margin at the anterior or broader end jagged, at the poste- 

 rior or narrower end abruptly truncated ; there is no notch, groove, 

 slit or channel. Length 1*75, diam. 0'3 inch. 



Body whitish, with a faint tinge of brown ; mantle very thin, 

 forming a collar, which encircles the inside of the upper part of 

 shell; tentacles very numerous, with pear-shaped tips, issuing be- 

 tween the mantle and the shell ; foot, when at rest, conical, having 

 a semi-circular lobe or flap on each side, so as to give it a tricuspid 

 appearance ; the lobes are fringed or puckered at the edges (Jef- 

 frey*)- 



In D. candidum the apical slit varies from a length of several 

 millimeters to none at all. In one shell before us it is on the side 

 of the tube. An abnormal specimen collected by the Fish Com- 

 mission is bent spirally, the torsion amounting to about 80. 



Compared with D. capillosum this species is more glossy, more 

 curved, with the grooves between the striae far less impressed, com- 

 paratively superficial. 



Figs. 27, 28, of PL 8, are copies of Verrill's illustrations of D. 

 solidum. The figures on PL 15 were drawn from northwest Atlan- 

 tic specimens dredged by the IT. S. Fish Commission. 



D. ERGASTICUM Fischer. PL 15, figs. 35, 36. 



Shell large, thick, conic, little curved, white usually encrusted 

 with ferruginous substance ; posterior end very acute, exteriorly 

 costulate striate all around, strise close, about 40 in the region of the 

 slit, acute, narrow, prominent; becoming flat in the middle of the 

 shell, and at the aperture obsolete ; the growth-strise stronger near 

 the aperture. Slit linear, long, on the convex side. Aperture ex- 

 actly circular, little oblique, ivory-like and thick inside. Length 

 91, diam. of aperture 10, length of slit 15 mill. (Fischer). 



Gulf of Gascony and Atlantic, in 400-1900 meters (Travailleur 

 and Caudan Exp.). 



D. ergasticum FISCHER, Journ. de Conchy!., 1882, p. 275. Lo- 

 CARD, Kes. Sci. de la Campagne du "Caudan" dans le Golfe de 

 Gascogne, fasc. i, p. 170, pi. 6, f. 1, from Ann.de 1'Univ.de Lyon 

 (1896). 



According to Locard the riblets in fully adult D. ergasticum are 

 visible the entire length of the shell from apex to aperture, and the 



