80 JOURNAL OF THE NEW JERSEY 



S. Shells about 3 times as long as high ; umbones about central 



19. Psammohiidce . 



S. Shells not 3 times as long as high ; surface covered with elevated radi- 

 ating ridges ; chalky white ; umbones near anterior end.J7. Petricolidw. 

 S. Shell about twice as long as high; epidermris polished and with a 



notched border extending beyond the edge of the thin shell 



28. Solemyidce. 



S. Shell thick with a thick black epidermis ; external ligament promi- 

 nent and on the shorter end of the shell SI. Saxieavidce. 



T. Length decidedly greater than height 82. Pholadidce. 



T. Length and height nearly equal ; small shells usually about 6 long never 

 over 12 long S8. Teredidce. 



KEY TO THE MARINE GASTROPODS. 



* Shell spiral, of one to many whorls. (H.) 



* Shell of one piece, flat, boat or cup-shaped, if somewhat spiral not forming 

 a complete whorl, (W.) 



* Shell straight or slightly curved, globular to tubular needle-shaped. (B.) 



* Shell oval-oblong, composed of 8 similar arched pieces or valves, over- 

 lapping each other ; the margins leather-like. (Y.) 



* Animal without any external or internal shell. (A. ) 



A. Free swimming, pelagic animals with two wing-like projections from 



the sides of the head 36. Clionidce. 



A. Creeping animals with a broad disk called a foot. (Sea Slugs.) (O.) 

 B. Shell transparent or nearly so, closed at the posterior end which is quite 



sharp pointed ; animals with wing-like projections; free swimming 



■ 85. Cavoliniidce. 



B. Shell tubular, open at both ends ; deep water. Genera Dentalium and 



Cadulus in Dental idae. 

 B. Shell not translucent ; tubular, operculated, curved, closed but blunt at 



the posterior end; our species not over 3 long 61. Ccecidce. 



C. Animal either without gills or the gills concealed on the right side be- 

 tween the mantle and the foot. {Or.) 

 C. Animal with exposed gills on the back. (D.) 

 D. Gills either pinnate or bipinnate, forming a crown upon the back. (F.) 

 D. Gills simple to branching tree like, situated more or less along the sides 

 of the body. (E.) 

 E. Dorsal tentacles retractile into sheaths 45. Tritoniidce. 



