FRESH-WATER MALACOSTRACA OF ONTARIO 

 SESSIONAL PAPER No. 39b 



155 



This species is . readily distinguished from our other Crustacea by its 

 laterally compressed, dentate rostrum (see figure), by the sharp bending of the 

 abdomen at the third abdominal segment and by the enlarged lateral plates of the 

 second abdominal segment. There are from 7 to 9 teeth on the dorsal edge of the 

 rostrum and from 1 to 3 on the ventral edge. Length up to 38 mm. 



Genus Cambarus. 



All our crayfishes belong to the genus Cambarus. One species of the allied 

 genus A stacus or Potamobius occurs on the coastal slope of British Columbia. 



We have two monographs of the crayfishes of North America, one by Hagen 

 (1870), and another by Faxon (1885). Ortmann (1905) has given the most 

 recent revision of the group. 



The crayfishes are bottom forms, living altogether in shallow water, not de- 

 scending deeper than a few fathoms. For the most part they shelter them- 

 selves during the day under stones, plants, etc. or in holes excavated in the mud. 



Eight species are properly referable to our region. Four of these have already 

 been reported from Ontario and to these I can add two. The other two I have 

 not seen. 



Outside of Ontario, C. bartonii has been reported from New Brunswick and 

 Quebec, and C. virilis from several points in the middle west (Lake Winnipeg, 

 Saskatchewan River, Red River). 



Key to the Species. 



Aj First abdominal appendages of male hooked (Fig. 8, e-f). Rostrum without 

 lateral teeth (Fig. 9, d, e— f). 



Fig. 8. 



Bi Areola of moderate width (Fig. 9, e) C. bartonii. 



Bj Areola nearly or quite obliterated in the middle (Fig. 9, d). 



Ci Dactyl of first legs excavate at base on outer side (Fig. 11, sl).C. fodiens. 



Cj Dactyl of first legs not excavate at base (Fig. 11, b) C. diogenes. 



