EAST AMERICAN SCAPHOPOD MOLLUSKS. 7 



and I am equally indebted to Mr. William F. Clapp, in charge of the 

 collection of mollusks in the Museum of Comparative Zoology in 

 Cambridge, Massachusetts, for his courtesy in sending me all the 

 American Scaphopods of that collection. 



CLASSIFICATION OF THE SCAPHOPODA. 



The class Scaphopoda includes but two families — the Dentaliidae 

 and the Siphonodentaliidae. The distinctions between them are 

 based upon (a) differences in the median tooth of the radula, (h) the 

 form of the foot, (c) certain quite definite shell characters.^ 



The Dentaliidae has the median tooth of the radula twice as wide 

 as long; a pointed conical foot surrounded by an epipodial process 

 resembling a wingshaped sheath, which is interrupted or slit, like the 

 break in a fold, on one side; a shell with greatest diameter at aperture. 

 The shell is almost always, to some extent at least, sculptured. 



The Siphonodentaliidae has the median tooth of the radula less than 

 double its length. The foot lacks any epipodial processes, and is 

 either a slender vermiform organ or is expanded on the end into a 

 symmetrical disk with fluted or indented border. The shell, except 

 in one restricted group, wholly lacks sculptural features, being smooth 

 and glassy in texture, and it is generally contracted at the aperture. 



Family DENTALIIDAE. 



The family Dentaliidae possesses but one genus — Dentalium. This 

 has been subdivided into a number of subgenera based chiefly upon 

 apical characters of the shell. The actual value of these apical 

 characters for the purpose of classification, and therefore the value 

 of subgenera chiefly based upon them, is not altogether assured, but 

 in a genus embracing so many species some form of division is useful, 

 even though it be somewhat artificial. Any one character, if relied 

 upon to distinguish the larger groups, answers well enough for a time, 

 but it always seems ev'entually to invite trouble. The shell characters 

 that may be used better in combination for the larger or the smaller 

 groups are: Type of sculpture, the form of the tip, the degree of cur- 

 vature, the size and thickness of the shell, the position and form of 

 the apical slit.^ 



1 For detailed study of the anatomy of the Scaphopoda see Lacaze-Duthiers,IIistoriede rorginisation et 

 du developpement du Dentale. Aim. des Sci. Nat. (Zool.), vol. 4, pp. vi, vii, (1856-7); Simroth, Bromi's 

 Klassen und Ordnungen des Thier-Reiehs (new ed.), vol. 3, pp. 356-467, (1895); Lang, Text Book of Comp . 

 Anatomy (English translation by Bernard), Part 2 (1896) (see index for many references); Pilsbry and 

 Sharp, Tryon's Manual of Conchology, vol. 17 (1897-8) (see pp. xi-xiv for references to literature); Pelseneer, 

 Mollusca, vol. 5 of Treaties on Zoology (Lankester), pp. 197-204(1906) (see bibliography on page 204). The 

 earlier researches of Deshayes, Sars, and others are full}' reviewed in the works mentioned. 



2 For discussion of the relative values of subgeneric characters in the Scaphopoda see Filsbry and Sharp 

 in Tryon's Manual of Conchology, vol. 17, p. ix of the introdiiction, also p. xxix. See also Dall in Trans- 

 actions of the Wagner Institute, vol. 3, part 2, p. 435. 



