FRESH-WATER MALACOSTRACA OF ONTARIO 147 



SESSIONAL PAPER No. 39b 



Asellus communis Say. Fig. 1, c, d. 



Harger in Smith, 1874, p. 657; Richardson, 1905, p. 420. 



Abundant nearly everywhere in shallow water among weeds and frequently 

 found in stagnant pools. Richardson records it from Massachusetts to Michigan 

 on the north. 



Localities. — Georgian Bay: Go Home, Fitzwilliam Id. (R) ; Waubaushene, Go 

 Home, Shawanaga, French River, Fitzwilliam Id. (Wo). Lake Ontario: Toronto. 



Fig. 1. 



This species differs from other members of the genus in having the head broad- 

 est about its middle, the uropods about as long as the last segment, distinct 

 epimera on all the thoracic segments and the palmar margin of propodus of first 

 gnathopod with one or two teeth. Length up to 11 mm. (15 mm. Harger). 



The specimens that I have examined do not agree perfectly with the de- 

 scription of Asellus communis given by Richardson. They are in many respects 

 intermediate between her descriptions of that species and of Asellus intermedius. 

 With the latter my specimens agree in having a distinct lobe at the posterolateral 

 angle of the head, and the antennule extending to the middle of the last segment 

 of the peduncle of antenna. According to Richardson, the flagellum of the 

 antennule is composed of fourteen articles in communis and of nine articles in 

 intermedius. In my specimens they vary in number from nine to twelve. The 

 inner branch of the uropods is sometimes of the same width as the outer as 

 described for intermedius and sometimes twice as wide as the outer as described 

 for communis. It is to be doubted whether these are distinct species. Richard- 

 son copied Smith's figure of Asellus communis, which does not agree with her 

 description of that species but agrees more nearly with her description of the 

 other species. Until the matter is- settled by further study, I consider it best to 

 use Say's name, which is the older. 



396—10 II 



