EAST AMERICAN SCAPHOPOD MOLLUSKS. 95 



Genus CADULUS Philippi, 1844. 



1844. Cadulus Philippi, Enum. Moll. Sicil., vol. 2, p. 209. 



Small, white, sculptureless Scajyhopods, which are more or less arcu- 

 ate, generally swollen, or with an inflated bulging area in the middle 

 portion of the shell or near the anterior aperture; the aperture is more 

 or less contracted and usually very oblique. The apical aperture is 

 proportionately quite large as compared with that of Dentalium; it is 

 either simple or cut by two or four slits. Section round or flattened. 

 Occasionally an internal circular rib is developed just within the api- 

 cal orifice. 



The genus is somewhat artificially divided into four subgenera as 

 follows : 



1. Apex with 2 deep slits Dischides. 



2. Apex with 4 deep slits Potyschides, page 96. 



3. Apex with 2 or 4 very shallow, broad slits .Platyschides, page 104. 



4. Apex simple (unslit). 



(a) Obese, dorsal, and ventral arcs both convex Cadulus, page 141. 



(6) Slender, one arc convex, the other more or less concave. . .Gadila, page 130. 



Species showing extreme characters are clearly and easily referred to 

 a subgenus, but there are species that could be placed in more than one. 

 The apical features, when normally present, are not infrequently 

 broken or worn away in poor or senile specimens. 



The genus is represented in east American Atlantic waters in all its 

 faunal areas and in all depths from near the tidal zone to the abyssal 

 depths. The mollusk lives in sandy and muddy stations and often in 

 great individual quantity. 



As a rule the species are not very widely distributed, but certain 

 exceptions are notable. Cadulus platensis, for instance, is found oft" 

 the Argentine coast to Georgia, and is further extended through slight 

 shell differences into the eastern Atlantic, north to Great Britain, 

 where, with relatively slight modification, it is O. tumidosus Jeffreys. 

 This is judging only from the shell characters. 



The amount of variation in any one species is usually slight, except 

 in the bulbous species under the subgenus Cadulus. Among some of 

 these the degree of swelling may differ somewhat in individuals, but 

 even here the seemingly great'variation is exaggerated to the eye by 

 breakage of the ends of the shells causing the shortened specimens to 

 appear more inflated. At present almost nothing is known of the 

 ecology of the genus. 



In the descriptions following, color, sculpture, and all features re- 

 lating to the shell texture will be omitted, as these remain essentially 

 the same; i. e., color white; sculpture none; texture vitreous and more 

 or less translucent or transparent. In some cases the clear vitreous 

 shell is modifled by circular deposits of shelly material, causing alter- 

 nate rings of more or less translucency. These are not, however, 



