SCAPHOPODA. 



Shell tubular, open at both ends, attenuated at the posterior end, more or less curved, 

 the concave side dorsal. 



I. Family DENTALIIDAE. 



Width of the median tooth of the radula double its height. Tooth with an encircling 

 epipodial sheath which is discontinuous, interrupted on the side ne.xt to the head. Shell greatest 

 in diameter at the oral opening. 



II. Family SIPHONODENTALIIDAE. 



Width of median tooth much less than double its length, generally less than the length. 

 Foot vermiform, capable of expansion into a terminal or subterminal rosette-like disk, not inter- 

 rupted dorsally. Shell generally smooth, or if ribbed tri- or pentagonal, often inflated. 



I. Family DENTALIIDAE. 



Dentalium L. 1758. 



The genus Dentalmm is coextensive with the family Dentaliidae. 



Key to subgenera. 



I. Shell longitudinally ribbed or striated. 



a. Number of the ribs near apex generally not exceeding 20 . Dentalium s. s. . p. 7 



a' Ribs more numerous, often a long slit on the convex side . Fissidentalium . . p. 36 



a" . Shell square at and near the apex Tesseracme . . . p. 39 



a'". Shell finely striated near the apex, anteriorly quite smooth. Antalis^ Graptacnie. p. 43 



II. No longitudinal sculpture. l^"*^^ 44 



a. Shell triangular or subtriangular in section Gadilina . ... p. 49 



a}. Shell conspicuously laterally compressed Bathoxiphus . . p. 48 



