148 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 

 Mancasellus tenax (Smith). Figs. 1, a, b: 2. 



Asellus tenax Smith, 1871, p. 453. 



Asellopsis tenax Harger in Smith, 1874, p. 601. 



Mancesellus tenax Underwood, 1890, p. 359; Richardson, 1905, p. 415 



This species is less abundant than the preceding one and is more restricted 

 to open and pure water, although one record is from a small inland lake. It has 

 been reported as ranging from Lake Superior to the Detroit River. This range 

 must be extended to Lake Ontario. It is probably found throughout the entire 

 region of the Great Lakes. It has been found in as deep water as 30 fathoms 

 (Smith). 



Fig. 2. 



Localities. — Lakes Superior and Huron (Smith), 



Georgian Bay: Sydney Bay (Wiarton), Go Home (R); Sturgeon Bay, Shaw- 

 anaga, Tamarac Bay (Manitoulin Id.), Fitzwilliam Id. (Wo). 



Lake Ontario: Toronto Island. 



Stomachs of Coregonus clupeaformis (R), Perca flavescens (Forbes). 



In addition to the generic difference given in the key, this species is readily 

 distinguished from the preceding by the extended truncate epimera (not separate 

 from the segments) and by the head being much broader than long and with a 

 deep incision on each side (Fig. 1, a). Length up to 11-5 mm. (13 mm., Harger). 



From other species of the genus this differs in having deep lateral incisions 

 in the head, antennae about half the length of the body and the uropods about 

 two-thirds the length of the last segment. 



Two subspecies or varieties are distinguished, M. tenax tenax, the typical and 



