DENTALIUM-GRAPTACME. 91 



The following specific names are synonymous, in our opinion : D. 

 semistriatum Turton (1819), D. semipolitum Brod. & Sowb. (1829), 

 D. semi sti-io latum Guild. (1834), D. hyalinum Phil. (1846), D. lira- 

 turn Carp. (1857), and D. lirulatum Morch (1861). The known 

 geographic range includes the Gulf of Mexico and west coast of 

 Mexico and Lower California. While we have no doubt of the 

 correctness of the above synonymy, we give below, under separate 

 heading, a description of the west American race. 



Var. SEMIPOLITUM Broderip & Sowerby. PI. 16, fig. 54. 



Shell slender, moderately or decidedly curved, attenuated toward 

 the apex ; rather thin, milk white and very glossy. Sculpture : 

 deeply enr/raved tvith very numerous, fine, dose, subeqnal, longitudinal 

 strice, extending from the apex dowmvard one-third to two-thirds the 

 shell's length (and of course covering the entire length of young 

 shells) ; the remaining one- or two-thirds smooth and polished, bril- 

 liant, scarcely showing growth-lines. Aperture circular, the peri- 

 stome thin. Anal orifice minute and round, no notch or slit. 



Length 26, diam. of aperture 2*6 mill. 



Length 29*5, diam of aperture 2*9 mill. 



La Paz ; Acapulco ; Mazatlan ; north to Mulege Bay, Boca de 

 los Piedras and San Ignacio Lagoon, Lower California, and San 

 Diego, California. 



D. semipolitum. B. & S., Zool. Journ., iv, p. 369 (1829). — ?i). semi- 

 politum Sowb. Jr., Thes. Couch., iii, p. 100, pi. 224, f. 23 ; Conch. 

 Icon., xviii, pi. 4, f. 19. — D. semipolitum Sowb. Carpenter, Suppl. 

 Rep. Moll. West Coast N. A., Brit. Asso. Adv. Sci. for 1863, pp. 612, 

 648, 666 (1864) ; and in Smiths. Misc. Coll., No. 252, pp. 98, 134, 

 152. — D. semipolitum Cp., Stearns, Proc. U. S. Nat. Mus., xvii, p. 

 158 (1894). — D. hyalinum Phil., Zeitschr. f Malak., iii, p. 55 

 (1846). Not I), hyalinum Ph., Carpenter, Mazatl. Catal., p. 188. 

 — D. liraturn Carpenter, [bid., p. 188 (young shell). — Sow^erby. 

 Thes. Conch., iii, p. 101, pi. 224, f. 32 ; Conch. Icon., xviii, pi. 5, f, 

 34. — D. lirulatum Moerch, Malak. Bliitter, vii, p. 177 (1861). 



Compared with D. acicalum of the same length, a larger part of 

 the surface of D. semipolitum is seen to be striated. It is a very 

 beautiful shell, quite constant in the fine sculpture of the smaller 

 end, though, as in all species, with diverse ornamentation at the two 

 ends, the extent of the sculptured and smooth portions varies regu- 

 larly with age, and somewhat among adults. Quite young and half- 



