DENTALIUM-GRAPTACME. 89 



erectum G. B. Sow. and D.splendidum Desh. ; a little stumpier and 

 more curved than the first, and less so than the second ; it is much 

 more longitudinally ribbed and less polished than either. Than D. 

 lessoni Desh., it is much more attenuated, and never so strongly 

 ribbed longitudinally ; than D. inversum Desh., it is more strongly 

 and persistently striate longitudinally. The young shell is per- 

 plexiugly like that of D. entalis var. orthrum Wats., but is a little 

 straighter, broadens more slowly, and the ribs project more sharply. 

 In maturer specimens this species is obviously much more attenu- 

 ated than the former. 



D. EBOREUM Conrad. PI. 16, figs. 47, 48, 49, 55, 56. 



Shell slender, attenuated posteriorly, gently curved, shining, 

 white. Sculpture : extremely close, fine, but rather deeply en- 

 graved longitudinal striae toward the apex, the larger part of the 

 shell smooth and glossy. Aperture slightly oblique, circular; peri- 

 stome thin. Anal orifice small and round. No notch or slit. 

 Length 20, diam. of aperture 1*8, of apex 0*35 mill. 



West coast of Florida : Tampa (Conrad) ; Marco (Hemphill) ; 

 Sanibel Island (Johnson). 



D. eboreum CONEAD, Proc. Acad. Nat. Sci. Philadelphia, iii, p. 

 27 (1846). 



The description and figures are from Conrad's type specimen in 

 the collection of the Academy. It is allied to D. semistriatum 

 Turt., but is less curved and more slender. 



Specimens collected at Sanibel Island by Mr. C. W. Johnson, 

 two of which are illustrated on pi. 16, figs. 55, 56, indicate that the 

 species attains a much larger size than the types. As the figures 

 show, they vary much in arcuation ; and they have lost the posterior 

 striation by truncation in the course of growth. The shells figured 

 measure : 



Length 31, diam. at aperture 2'5, at apex 0'8 mill. 



Length 27'4, diam. at aperture 2 '2, at apex 0'75 mill. 



D. LEPTUM Bush. PI. 16, fig. 50. 



Shell of moderate size, very slender, slightly curved posteriorly, 

 rather thin, delicate, with a very smooth and glossy surface, destitute 

 of sculpture, except at the posterior end, which is covered with numer- 

 ous, very fine, raised, longitudinal lines visible only under the lens. 

 Anterior aperture round, with a sharp, thin edge ; posterior aper- 

 ture somewhat thickened, very small, round, slightly oblique, with 



