22 DENTALIUM. 



D. texasianum Phil. Shell little curved, slowly increasing in 

 diameter, white, six-angular ; interstices of the ribs flat, plain at the 

 apex, but toward the base with 1,2 or 3 elevated striae. Length 10 

 lines, diam. of base scarcely 1, of apex f. (Phil.'). 



Galveston, Texas (Roemer). 



D. texasianum PHIL., Zeitschr. f. Malak., 1848, p. 144 (March, 

 1849). 



Readily distinguished from other six-angled species by the size, 

 the rate of increase, and the interstices of the ribs becoming flat 

 toward the aperture and delicately striate there (Phil.'). 



D. amerieanum Chenu. (PL 5, figs. 71, 72). Shell with six prin- 

 cipal projecting ribs, with weak intermediate ribs or none ; trans- 

 verse striae distant. 



Length 23, diam. 1'8 mill, (from fig.). 



Length 28, diam. 2'8 mill, (from fig.). 



Shores of America (Chenu). 



D. amerieanum CHENU, Illustr. Conch., i, p. 1, pi. 4, f. 9, 10. 



Chenu's description and figures are here given for what they may 

 be worth. We had thought to identify amerieanum with disparile 

 Orb., but in view of the strongly 6-angled section of the former, this 

 is hardly possible. If the locality is correct we are disposed to con- 

 sider it the same as D. gouldii Dall. 



D. PICTETI Deshayes, n. sp. PI. 11, fig. 87. 



Shell narrowly elongate, slightly arcuate ; white, translucid, reg- 

 ularly 6-angulate, the angles projecting, equal and equally spaced, 

 very narrow ; the interstices smooth, alternately marked with trans- 

 lucent and opaque-white. Aperture symmetrical, six-angled; peri- 

 stome thin, transverse. Posterior orifice small, circular, somewhat 

 bi-labiate. 



West Indies f (coll. Delessert). 



D. amerieanum var. c, CHENU, Illustr. Conch., pi. 6, f. 35 (not 

 pi. 4, f. 9, 10). D. picteti DESHAYES in MS. card catalogue of Den- 

 talium. 



Deshayes, from whose MS. the above diagnosis is taken, states 

 that Chenu lumps two if not three species under the name D. amer- 

 ieanum. The present form seems to be distinct from D. disparile in 

 the six continuous prominent ribs with no interstitial riblets, and in 



