174 



ZOOLOGY 



APPENDIX TO CHAPTER XI 



Spirulidw 



VermetidcB 



KEY TO THE PRINCIPAL FAMILIES OF MARIXE-SHELLED 

 GASTROPODS OF THE ATLANTIC COAST OF THE UNITED 

 STATES, ADAPTED FROM A. C. APGAR 



a i. 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] 

 bo. Spire dextral. 



Ci. Operculated ; aperture not over \ area of 



shell. 



d\. Anterior margin of aperture entire. 

 i. Shell tubular ; spiral at apex, 

 irregularly twisted near aper- 

 ture ..... 

 e>2. Shell regularly spiral, elongated ; 

 width less than 1 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 . 

 / 2 . Whorls about 5; minute shell, 

 less than 5 mm. long ; width 

 about | length ; aperture 

 about i length ; apex blunt 

 / 3 . Whorls 5-10 ; shells elon- 

 gated, conical, turreted ; 

 aperture ^-| ; length of 

 shell of our species 4-10 

 mm. long .... 

 63. Shell regularly spiral, shortened ; 

 width nearly as great as or 

 greater than length ; whorls 



ScalariidcB 



Rissoidce 



Pyramidellidce 



