DENTALIUM-GRAPTACME. 87 



D. sericatum DALL, Bull. M. C. Z., ix, 1881, p. 37 ; xviii, Blake 

 Moll., p. 423, pi. 26, f. 1 ; Bull. U. S. Nat. Mus., 37, Catal. Mar. 

 Moll. S.-E. U. S., p. 76, pi. 26, f. l.D. semistriolatum var. B, 

 GUILDING, Trans. Linn. Soc. Lond., xvii, p. 34, pi. 3, f. 6 (1834). 

 D. nebulosum Lin., DESK., Mem. Soc. Hist. Nat. Paris, ii, p. 369, 

 pi. 16, f. 20 (1825). SOWERBY, Thes. Conch., iii, p. 98, pi. 225, f. 

 58 (1860) ; and in Conch. Icon., pi. 7, f. 53 (good). Not D. nebu- 

 losum Gmeliu, Syst. Nat. (13), p. 3738. 



Remarkable for the zig-zag white rings of the young, and the 

 position of the slit, which is generally more lateral than ventral, 

 although intermediate between the convex and lateral sides of the 

 shell. D. cocconii Sharp & Pilsbry (D. dispar Mayer in Cocconi, 

 not Sowb.), has a similar lateral slit. The young are densely 

 striated longitudinally and generally without a slit, and some old 

 specimens have swollen rings as in D. eburneum, but slighter. 



We do not follow Deshayes' identification of this with Gmelin's 

 nebulosum, because the description of that, as well as the locality, 

 indicate a different form. Some authors have referred it to D. vul- 

 gare. Gmelin's description, which is not elucidated by citation of 

 figures, is as follows : 



" D. testa arcuata,laevissima, alba, fulvo, maculata, uebulosaque. 

 Habitat in Mari Siculo, fasciato affine, ac testa magis arcuata, 

 longiore et tenuiore." 



Ball's description of the single specimen dredged by the * Blake ' 

 is quoted below. We consider it a young shell in which the charac- 

 ter of being longitudinally striate throughout would disappear in 

 the adult form. The alternation of translucent bluish with opaque 

 white bands is but poorly represented by the figure, which shows 

 the pattern merely. We have compared the type of sericatum with 

 the adult shells described above, and have before us a full series 

 connecting the sharply zig-zagged young form with the ring-clouded 

 adults. The locality given by Deshayes for his nebulosum is incor- 

 rect. 



D. sericatum Dall. (PI. 7, fig. 12). " Shell small, very thin, acute, 

 slightly curved, rather rapidly enlarging, covered with fine, sharp, 

 close-set longitudinal grooves, with narrow thread-like interspaces 

 separating them, to the number of thirty-six on the middle and 

 about fifty at the oral end of the shell ; plane of oral aperture at 

 right angles to the axis, both apertures circular, simple; color 



