] 80 M. Deshayes' Monograph of Dentalium. 



L Shell not cleft at its posterior extremity. 

 A. Striated or ribbed longitudinally. 



1. D. ELEPHANTINUM, Linn. D. testd duodecim costatd, angulatctj 

 subrectd, albidd ; costd minore unicd inter alias. 



D. elephantinum, Auct. (baud Lamarck vel Sowerby.) 



D. rectum, Gmel. p. 3738. n. 12. 



Habitat in mari Indico, necnon in Mediterraneo. — Foss. in Italia et 

 Austria. 



Shell large, tubular, rather broad at its base, nearly straight or very 

 slightly curved, white with transverse zones or pale green ; constantly 

 presenting at its apex twelve symmetrically placed ribs, between each 

 of which a small one is soon interposed, which becomes at the base 

 nearly as thick as the primary ones, thus giving at the thicker extremity 

 the appearance of twenty-four ribs. In the fossil variety from Austria, 

 the ribs are all equal from their origin. 



Length from 3 to 3^ inches. Diameter of the base from six to seven 

 lines. ^ 



2. D. ARCUATUM, Linn. D. testd albo-virescente, tereti, arcuatd, decern 

 costatd, costis inferiorihus majoribus ; stria unicd inter castas. 



D. elephantinum. Lam., Anim. sans vert. v. p. 343, n. 1. Sowerby^ 

 Genera of Shells, No. XV. f. 1. 



Habitat in Mari Indico. 



Shell large, arcuated, green at its base, whitish, or yellowish green at 

 the apex. Ribs prominent, generally ten, occasionally only nine ; the 

 dorsal ones flattened as though broken down, the ventral ones much more 

 prominent ; between each of the ribs is generally seen a slightly marked 

 stria. Apex not very acute. Margins of the opening thin, cutting, fes- 

 tooned on the inside by the notches in each of the ribs. 



Length upwards of 3 inches. Diameter of the base 5 lines. 



3. D. SEXANGULARE, Lam. D. testd tereti, arcuatd, subulatd,. duode- 

 cim costatd ; costis sex eminentioribus ; striis transversis minimis. 



D. sexangulum. Gmel., p. 3739, n. 21. 



D. elephantinum. Sowerby, Genera, No. XV, f. 2.. 



