DENTALIUM. 35 



angles pinched up into narrow ribs, which continue to or beyond the 

 middle of the shell, gradually decreasing; intervals at first flat or 

 somewhat concave, soon becoming convex midway between the ribs, 

 and when perfectly preserved showing faint longitudinal striation at 

 this place ; the convexity increases until the latter third of the shell 

 is cylindrical, and sculptured ivith rather conspicuous, oblique growth- 

 lines only. Aperture oblique, circular. Apex minute, with a 

 circular orifice ; no slit or notch. Length 30'5, diam. at aperture 

 2-9, at apex 0'6 mill. 



Gulf of Nicoya and Puerto Portrero, W. coast Central America ; 

 also Xipixapij west coast Colombia (Cuming), 10-16 fms., sandy 

 mud. 



D. tesseragonum G. B. SOWERBY, P. Z. S., 1832, p. 29. D. tetra- 

 gonum SOWB. JR., Thes. Conch., iii, p. 103, pi. 224, f. 21, 22 (1860) ; 

 and in Conch. Icon., xviii, pi. 4, f. 20a, b. ? CARPENTER, Rep. 

 Brit. Asso. Adv. Sci. for 1863, p. 666; Moll. West Coast N. A., p. 

 152. Not D. tetragonum Brocchi, 1814. 



The original description here follows: Shell thin, milk-white, 

 smooth, at first tetragonal but becoming cylindrical by the disap- 

 pearance of the angles ; very delicate growth-lines forming sub- 

 hyaline rings. Length 0*8, diam. O'l inch. (G. B. /S.). 



Var. : angles indistinct ; growth-lines forming rings (G. B. /S.). 



Mr. Sowerby changed the name of his fathers species in 1860 

 without assigning any cause, or even mentioning that a change had 

 been made. The etymology of the original name is obvious, and we 

 do not see that such radical emendation is called for, the more be- 

 cause the specific name tetragonum had already been used by Broc- 

 chi. 



Carpenter reports tetragonum Sby. from Margarita Bay, Pacific 

 coast of Lower California in about N. lat. 24, specimens collected 

 by one of Harper Pease's collectors. They may possibly be refer- 

 able to D.fisheri, q. v. There are some specimens in the collection 

 of the Academy safd to be from Rio Janeiro, collected by the U. S. 

 Exploring Expedition. We do not know whether the locality is 

 authentic or not, but it seems doubtful. There were, however, 

 several species of this type in the Antillean Miocene fauna. 



D. QUADRANGULARE Sowerby. PI. 5, fig. 77. 



Shell small, white, quadrangular, the angles rather acute, inter- 

 stices striated. Aperture four-cornered. Length '8, diam. '15 inch. 



