AMPHIPODA 369 



CALLIOPIUS Lilljeborg. Both pairs of gnathopods large and of 

 equal size ; terminal abdominal segment slender and not split : 2 species. 



C. laeviusculus (Kroyer) (Fig. 581). First and second antennae of 

 nearly the same length; eyes large; length 16 mm.; color light green: 

 Cape Hatteras to Greenland, in tide pools 

 and among seaweed; Europe; North Pacific. 



FAMILY 5. GAMMAEIDAE. 



Both pairs of antennae long, the first 

 antennae usually longer than the second and 

 with a secondary flagellum which is a small 

 side branch of it; mandible with a palp; 



both pairs of gnathopods usually of the same size; terminal pleopods 

 extending beyond the others: over 50 genera and 250 species, largely in 

 fresh and brackish waters. 



Key to the genera of Gammaridae here described : 



Oj Last 3 abdominal segments with small bunches of hairs along hinder margin. 



bi First 3 abdominal segments not extended behind 1. GAMMARUS 



by First 3 abdominal segments each extended behind as an acute tooth. 



2. CARINOGAMMARUS 



a a No such bunches of hairs on these segments 3. ELASMOPUS 



1. GAMMARUS Fabricius. Telson deeply cleft; last 3 abdominal seg- 

 ments with bunches of small hairs: over 30 species; in salt and fresh 

 water; 6 fresh- water species in the United States. 



Fig. 582 Fig. 583 



Fig. 582 Gammarus locusta (Paulmeier). Fig. 583 Gammarus faciatus (Paulmeier). 



G. locusta (L.) (Fig. 582). First antennae longer than the second; 

 secondary flagellum with about 8 joints; length 20 mm.; color greenish: 

 Arctic Ocean to New Jersey, being very common under stones and in 

 seaweed along the seashore; Europe. 



G. annulatus S. I. Smith. First antennae shorter than the second; 

 length 15 mm.; no lateral hairs on the fourth abdominal segment: Long 

 Island Sound to Bay of Fundy, 



