DENTALIUM-GRAPTACME. 95 



perlongum Dall is not so much as two-thirds of the breadth of Den- 

 talium acutissimum. Contrary to Mr. Ball's statement, however, the 

 two species agree in having the anal fissure on the convex side. 



In reference to the form of the apex, it may be observed that the 

 separation of the Dentalia by the absence (Dentalium) or presence 

 (Entalis) of the cleft-process cannot be maintained. In Dentalium 

 abyssorum Sars there are some with a fissured process, some with a 

 fissure without any process, some with neither fissure nor process. 

 There are cases in which the fissure is very regularly formed, in 

 others it looks as if it had been gnawed, in others it resembles a 

 break ; sometimes it is on the convex curve, as in the general case, 

 sometimes on the concave as in Dentalium inversum Desh. and in 

 Dentalium subterfissum JefFr. ; sometimes it is irregularly lateral as 

 occasionally in Dentalium agile Sars ( Wats.). 



D. INVERSUM Deshayes. PL 21, figs. 47, 48, 49. 



Shell rather lightly curved, small, extremely slender, the length 

 about 16 times the greatest diameter ; translucent white, clouded 

 with opaque white, and becoming reddish toward the apex ; very 

 glossy. Sculpture, very fine and regular longitudinal striation near 

 the apex, the greatest part of the shell smooth, free from sculpture, 

 with very slight variceal rings as in D. eburneum but far less marked. 

 Aperture circular, the peristome thin. Anal orifice minute, round, 

 with a deep, narrow slit or a shorter notch, in the middle or excentric 

 on the concave side. Length 30, diam. of aperture 1*9, of apex 0'6 

 mill. ; length of slit 1*8 mill. 



Gulf of California (W. Newcomb, in coll. Acad.) ; Habitat un- 

 known (Desh., Sowb.). 



D. inversum DESH., Mem. Soc. Hist. Nat. Paris ii, p. 370, pi. 16, 

 f. 21, 22 (1825). SOWERBY, Thes. Conch., iii, p. 99, pi. 225, f. 42 ; 

 and in Conch. Icon., xviii, pi. 7, f. 51. E. A. SMITH, P. Z. S., 1871, 

 p. 738. 



Remarkable for having the slit on the concave side. Otherwise 

 the species is not very unlike D. semij)olitum. D. sectum Desh. 

 differs in being less attenuated posteriorly, with differently formed 

 apex and slit. 



One specimen from the Gulf of California, which we refer to this 

 species, has the apical notch formed as in many D. entails, with a 

 slightly projecting rim around the ovate orifice, slit not median, but 

 decidedly excentric on the concave side. This specimen occurred 

 with D. semipolitum B. & S. 



