174 



ZOOLOGY 



APPENDIX TO CHAPTER XI 



KEY TO THE PRINCIPAL FAMILIES OF MARINE-SHELLED 

 GASTROPODS OF THE ATLANTIC COAST OF THE UXITED 

 STATES, ADAPTED FROM A. C. APGAR 



ai. Shell spiral, of one to many whorls. 



61. Spire in a single plane, and whorls not in con- 

 tact. [A cephalopod shell ; liable to be 

 mistaken for a gastropod-shell, page 172] Spirit I idee 



6 2 - Spire dextral. 



Ci. Operculated ; aperture not over \ area of 



shell. 



d\. Anterior margin of aperture entire. 

 e\. Shell tubular ; spiral at apex, 

 irregularly twisted near aper- 

 ture . . . . Vermetidce 

 C 2 . Shell regularly spiral, elongated ; 

 width less than length ; 

 whorls 5 or more ; angle of 

 spire less than 45 ; aperture 

 less than \ length of shell, 

 /i. Whorls rounded , almost sepa- 

 rated, crossed by elevated 

 longitudinal ribs ; aperture 

 oval ; lip continuous ; our 

 species over 10 mm. long . Scalariidce 

 / 2 . Whorls about 5; minute shell, 

 less than 5 mm. long ; width 

 about i length; aperture 

 about J length ; apex blunt Eissoidce 

 / 3 . Whorls 5-10 ; shells elon- 

 gated, conical, turreted ; 

 aperture -$ ; length of 

 shell of our species 4-10 

 mm. long .... PyramideUidce 

 e s . Shell regularly spiral, shortened ; 

 width nearly as great as or 

 greater than length ; whorls 



