108 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



D. 2. Spire flat. 



Genus Planorbis. 

 E. 3. Shell large, high and sinistral. 

 F. 7. With wide shell concavity above. 



Planorhis trivolvis. 

 F. 8. With narrow deep concavity above, two carinse. 



Planornis bicarinatus, 

 F. 9. With no concavity above. Expansion behind the aperture. 

 Planorhis campanulatus. 

 E. 4. Shell small, depressed and dextral. 

 F. 10. Shell covered with bristles. 



Planorbis hirsutus. 

 F. 11. No bristles on shell. 



G. 1. Peripheral keel level with the top of shell. 



Planorbis dilatatus. 

 G. 2. Peripheral keel centrally placed. Shell lens-shaped. 



Planorbis exacuous. 

 G. 3. No peripheral keel. 



Planorbis deflectus. 

 C. 2. Spire elevated and sinistral or shell not spiral. 

 Family physidae. 

 D. 2. Spire elevated and sinstral. 

 Genus Physa. 

 E. 5. Shell large. 



F. 12. No sculpture on surface of shell. 



Physa heterostropha. 

 F. 13. Surface sculptured, spire short, suture not impressed. 



Physa ancillaria. 

 F. 14. Surface sculptured, spire more elevated, sutures impressed. 

 Physa gyrina. 

 E. 6. Shell small, usually whitish. 

 Physa integer niagarensis. 

 D. 4. Shell not spiral. 

 ^ Genus Ancylus. 



Ancylus parallelus. 

 B. 2. Operculate, operculum borne on the upper surface of foot and 

 closing the aperture of the shell when the animal is retracted. 

 C. 3. Spire very high, shell large, length 25-30 mm. 

 Family streptomatidae. 

 D. 5. Whorls towards apex not rounded. 



Goniobasis livescens. 

 D. 6. Whorls towards apex more or less rounded. 

 Goniobasis haldemani. 

 C. 4. Spire low or only moderately high. 

 D. 7. Umbilicus narrow. 



