176 



ZOOLOGY 



/ 4 . Shells less than 20 mm. long ; 

 aperture with a notch near 

 posterior end, formed by 

 outer lip not squarely meet- 

 ing body wall . 



fr,. Shells less than 15 mm. long ; 

 aperture entire at posterior 

 end ; narrow, and a little 

 less than -J the length of 

 the shell ; canal rather 

 short . .* 



e- 2 . Canal short or absent ; aperture 



notched, 

 /i. Shells large, 40 mm. or more 



long ; whorls rounded 

 / 2 . Shells 20-40 mm. long; 



whorls rounded 



/ 3 . Whorls flattened, surface 

 usually beaded ; aperture 

 over i length of shell 



Co. Non-operculated, or operculum very mi- 

 nute ; aperture with neither a canal 

 nor a notch at anterior end. 

 (I i. Aperture over f area and f length of 

 shell ; spire distinct, pointed ; shell 

 ear-shaped ..... 

 (?o. Aperture \ the area or more, and the 



full length of the shell. 

 Ci. Shell with 1 whorl, less than 2 

 mm. long .... 

 ?o. Shell with several whorls, under 



4 mm. long ; spire flat . 

 e-s. Several whorls, a pit in place of 



spire, over 6 mm. long . 

 t?s. Aperture less than ^ the area of the 



shell. 



e\. Aperture | to whole length of 

 shell ; spire distinct, usually 

 flattened ; under lip with single 

 fold or smooth 



Plwirotnmidce 



Columbellidce 



Philinidce, 

 Scaphandridce 



Bull idee 



TornatinidoB 



