146 MARINE AND FISHERIES 



5 GEORGE v., A. 1915 



Some of our Malacostraca are large enough to serve as food for man. The 



crayfishes and shrimps are marketed in many of the American states, 



but in Canada little use has been made of them. Our crayfishes are quite large, 



• but our shrimps are small. A species of shrimp that occurs in Ohio could doubtless 



be introduced here very readily. 



The Malacostraca are also of importance as serving as intermediate hosts for 

 many parasites which occur in fishes. 



The greater part of the material that I have examined was collected in the 

 summer of 1912 by Mr. R. P. Wodehouse at various points in the Georgian Bay. 

 To Dr. E. M. Walker, Mr. A. R. Cooper and Mr. A. D. Robertson I am indebted 

 for material from the Georgian Bay and from other points in Ontario. I have 

 indicated the sources of my material in the following way, — from Mr. R. P. Wode- 

 house— (Wo), from Dr. E. M. Walker— (Wa), from Mr. A. R. Cooper— (C), and 

 from Mr. A. D. Robertson — (R). 



Key to the Orders. 



Aj. Eyes sessile (Fig. 1). First thoracic segment fused with head. Remainder 

 (seven in number) free, with large appendages. 



Bj. Body compressed dorso-ventrally. Branchiae on abdominal append- 

 ages Isopoda. 



Bj. Body laterally compressed. Branchiae on thoracic appendages (Fig. 



3, br) Amphipoda. 



A2. Eyes pedunculated. The majority of the thoracic segments fused with the 

 head to form dorsally a carapace (Fig. 5). 



C^. Thoracic legs similar and biramous (Fig. 6). Several of the posterior 

 thoracic segments not fused with the carapace Mysidacea. 



Cj. Posterior five pairs of thoracic legs uniramous and large, anterior three 

 biramous and small. Not more than one thoracic segment free from carapace. 

 Decapoda. 



Order ISOPODA. 



For North America, this group has been monographed by Miss Harriet Rich- 

 ardson (see Bibliography). Only two fresh-water species have been reported 

 from the region of the Great Lakes. They belong to the family Asellidae. For 

 Canada no records have been published. The Isopods are to be found crawling 

 about in shallow water in a variety of situations (among weeds, under stones, etc.). 



Key to the Genera. 



A^. Mandible with palp (Fig. 1, d) •• Asellus. 



Aj. " without palp (Fig. 1, b) Mancasellus. 



