DENTALIUM-FISSIDENTALIUM. 81 



One specimen before us (fig. 35) has no slit, there being only a 

 slight notch on the inner margin of the anal aperture. It measures, 

 length 94, diameters of aperture 1O3 mill. In another shell 90 

 mill, long the slit has a length of 7*6 mill. 



D. RECTUM Gmelin. PI. 3, figs. 32, 33, 34. 



Shell nearly straight, slightly curved toward the anal end, solid, 

 whitish, with faint, wider, grayish zones, lusterless. Sculptured at 

 the anal end with about twelve larger alternating with an equal 

 number of smaller, rather high, narrow and sharply cut ribs ; this 

 number being increased toward the larger end by the intercalation 

 of numerous tertiary longitudinal riblets and striae; the whole sur- 

 face very densely aud finely microscopically striate in a longitudinal 

 direction, and decussated by equally fine incremental striae. Aper- 

 ture quite oblique, circular, thin-edged. Anal orifice small, circu- 

 lar, with a long, narrow slit on the convex side. Length 632,diam. 

 of aperture 12 mill. 



India (Desh.). 



D. rectum GMEL., Syst. Nat. (13), p. 3738 (1788). WOOD, Index 

 Testae, p. 191, pi. 38, f. \d (1818). Sows., Thes. Conch., iii, p. 101, 

 pi. 223, f. 1 (1860); Conch. Icon., xviii, pl.l.f. 4 (1872). DELES- 

 SERT, Rec. de Coq., pi. l,f. 3 (1841). D. elephantinum DESHAYES, 

 Mem. Soc. Hist. Nat. Paris, ii, p. 347, pi. 17, f. 7 (1825) exclusive of 

 fossil forms and var. a. Antalis recta CLESS., Conch. Cab., p. 25. 



The straight form, more rapidly increasing cone and alternating 

 ribs readily distinguish this from D. vernedei. 



The locality is very uncertain. Sowerby gives "Adriatic," which 

 is certainly wrong, unless, indeed, his figures really represent D. 

 delessertianum. We have a specimen said to be from the Gulf of 

 California. Compare D. delessertianum Chenu and D. philippii 

 Monts. not Chenu. 



The identification of this shell with Gmelin's species rests upon 

 his citation of a figure in Gualtier, reproduced with the embellish- 

 ment of color, and the omission of some of the sculpture, in Martini, 

 and a figure of Schroter's which seems to represent a crinoid stem. 

 While there is some doubt of the identity of D. rectum of modern 

 authors with that of Gmelin, it seems inadvisable to change. 



D. DELESSERTIANUM Chenu. PI. 6, figs. 78, 79. 



Shell large and solid, the apical third somewhat curved, remain- 

 der nearly straight or slightly recurved. Sculpture of 13-14 high, 

 6 



