Dentalium.\ SCAPHOPODA. 817 



and the absence of any definite head, eyes, or tentacles are points 

 which approximate them to the Lamellibranchia. More recent in- 

 vestigations, however, have shown that the Scaphopoda are more 

 nearly akin to the Gastropoda than to the Lamellibranchia. 



The Scaphopoda are marine burrowing molluscs, and, as a rule, 

 allow only the posterior extremity to project from the sand in which 

 they hide themselves. They feed on the lowest organisms, Diato- 

 macea, Protozoa, &c. 



There are about 150 living and 275 fossil species of Scaphopoda. 

 The living forms are distributed throughout all seas, from the littoral 

 to a depth of 2,500 fathoms. 



The fossil species extend back to the Middle Silurian, but are 

 most abundant from the Cretaceous onwards. 



Kara. DENTALIID^I, Gray. 



Animal having the foot conical, with a laterally expanded and 

 dorsally interrupted encircling sheath. Shell tubular, curved, with 

 the greatest diameter at the anterior aperture, and tapering evenly 

 to the posterior aperture. 



Genus 1. DKNTALIUM, Linne, 1758. 



Dentalium, L., Syst. Nat., ed. x, 1758, 785. Type : D. elephantinum, L. 

 Shell tube-like, curved, but not spiral, attenuated posteriorly ; 

 posterior orifice of the shell truncated, smaller than that at the an- 

 terior end ; dorsal face concave ; ventral face convex. No operculum. 

 Vernacular Name. Tusk-shell ; elephant-tooth. 

 Maori. Pipi-taiari. 



KEY TO 



A. Shell with longitudinal ribs. 



a. Ribs numbering 4 to 14, sometimes 20, strong near the 



apex, which is simple or with a very short notch. . DKNTALIUM. 



aa. Ribs numerous ; shell large and solid ; apex typically 



with a long slit, but sometimes simple. . . . FISSIDENTALITJM. 



B. Shell smooth or longitudinally ribbed ; apex with a pro- 



jecting pipe . . . . . . . . . . 



C. Shell smooth ; apex simple or with a short notch on the 



convex side . . . . . . . . . . 



Subgen. 1. DENTALIUM, s. str. 



Shell prismatic or decidedly ribbed, the ribs often very strong 

 toward the apex, where there are generally from 4 to 14, but some- 

 times as many as 20 ; apex with no notch or slit, or a short one. 



KEY TO SPECIES. 



A. Anterior end with 10 to 13 riblets . . nuw<in. 



B. Anterior end with about 18 riblets . . Hiittoni. 



