368 



CRUSTACEA 



H. dentata (Say) (Fig. 579). Hinder dorsal margin of the first 

 and second abdominal segments produced to form spines; length 6 



mm. : in fresh- water ponds in 

 the eastern states, where it is 

 one of the two common fresh- 

 water species of amphipods, 

 Gammarus fasiatus being the 

 other. 



Fig. 579 Hyalella dentata (Paulmeier) 

 first gnathopod ; 2, second gnathopod ; 

 periopods ; 4, pleopods ; 5, jumping legs. 



FAMILY 2. PONTOPOREIIDAE. 



First antennae but little 

 shorter than the second and 

 with a secondary flagellum; 



mandible with a palp; posterior periopods very broad and modified for 

 digging: about 8 genera and 22 species. 



HAUSTORITJS St. Miiller. Characters as above; small rostrum 

 present: 1 species. 



H. arenarius (Slabber) (Fig. 580). Length 18 mm.; color whitish: 

 Georgia to Cape Cod; on the seabeach near 

 high-water mark, where it burrows with 

 great rapidity; Europe. 



FAMILY 3. AMPELISCIDAE. 



First antennae some distance in front of 

 and at least half as long as the second; 4 

 eyes usually present; last 2 segments of 



abdomen fused together: a burrowing family with about 3 genera and 

 40 species. 



AMPELISCA Kroyer. Telson divided by a median cleft; 4 eyes 

 present ; first antennae about half as long as the second : about 25 species. 



A. macrocephala Lilljeborg. Postero-lateral margin of third ab- 

 dominal segment elongated; head usually as long as the first 3 thoracic 

 segments; length 15 mm.; color white: Vineyard Sound and north- 

 wards, living in tubes in the mud; Europe. 



A. compressa Holmes. Head considerably shorter than the first 3 

 thoracic segments; body very compressed; length 6 mm.: common from 

 Cape Cod to Cape Hatteras. 



FAMILY 4. CALLIOPIIDAE. 



First and second antennae of nearly the same length; periopods 

 rather strongly built, the last 3 pairs increasing successively in length: 

 about 15 genera and 30 species. 



