182 M. Deshayes' Monograph of Dentalium. 



White, subdiapnanous, moderately curved, with eight regular ribs, ex- 

 tending from the apex to the base, which are narrow, rounded, and per- 

 fectly symmetrical ; between them are two, or sometimes three, fine striae. 

 Transverse striae none, except occasional ir^.dications of growth. Apex 

 ])ointed, with a very small hole : opening regularly octogonal, cutting, 

 shghtly oblique. 



Length 1 inch 9 lines. Diameter of the opening 2i lines. 



6. D. ABBREVIATUM, Desh. D. testa minutd, abbreviatd, suhrectd, 



extremitate recurvd, septem angulatd, crassd ; aperturd rotimdd, redd, 



incrassatd. 



Foss. apud Suessones. 



Intermediate between this and the fourth section, the margins of its 

 opening being thickened, but no contraction existing below it. When 

 young it is straight, or nearly so, becoming, as it advances in age, more 

 curved, especially towards its posterior extremity, which is very acute and 

 perfectly smooth : a Utde above this commence the seven symmetrical 

 prominent angles, the median one of which is on the back ; they termi- 

 nate at the margin. Opening round and straight. Shell thick. 



Length 5 hnes. Diameter of the opening about | a line. 



''. D. VARIABILE, Desh. D. testd tereti, subarcuatd, albidd luteoldve; 



quinque ad novem costatd ; striis cxiguis interpositis. 



Habitat in mari Indico ? 



Small, slightly arched, generally not very acute, usually milk-white, 

 but rarely pale yellow. Ribs from five to nine in number, usually more 

 prominent on the concave than on the convex surface ; always most pro- 

 minent towards the apex, sometimes continuing to the larger extremity, 

 at others gradually disappearing, especially the dorsal ones, the ventral, 

 one, three, or five in number, remaining. In recent specimens the ribs 

 exhibit series of greyish white spots on the milk-white ground of the 

 shell. Striae, variable in proportion to the number of the ribs, being 

 more numerous when there are few, and vice versa : at first very fine, 

 becoming afterwards almost or quite equal in thickness to the ribs ; al- 

 ways continuing as far as the opening. 

 Length from 1 inch to 1 inch 2 lines. 



