366 CRUSTACEA 



H. medusarum (0. F. Miiller) (Fig. 575). Gnathopods covered 

 with setae on the sides ; length 12 mm. : found in Cyanea and other 

 jellyfish; coast of New England, north of Cape 

 Cod. 



FAMILY 2. PHRONIMIDAE. 



Head very long dorsoventrally, on the sides 

 and top of which are the large eyes ; no mandibular 



Fig. 575 Hyperia me- palp present; second antennae rudimentary in the 

 dusarum (Leunis). 



female: about 7 genera. 



PHRONIMA Latreille. Fifth pair of periopods with large chelae; 

 last thoracic segment elongated: 1 species. 



P. sedentaria (Forskal). Length 3 cm.: cosmopolitan; each indi- 

 vidual living in the transparent test of Salpa or Pyrosoma. 



SUBORDER 2. GAMMARIDEA. 



Seven free thoracic segments and pairs of thoracic legs; maxilli- 

 ped with a 2 to 4-jointed palp : about 40 families and over l f OOO species. 

 Key to the families of Gammaridea here described : 



Oi Three last abdominal somites normal and not fused together. 

 6i Body compressed and not flattened. 

 Ct Last pair of pleopods do not end in a hook. 

 d v First antennae usually shorter than second. 

 e t First antennae without secondary flagellum. 

 /! First antennae much shorter than the second. 



ff l Two eyes present 1. ORCHESTIIDAE 



02 Four eyes present 3. AMPELISCIDAE 



/, First antennae but little shorter than second 4. CALLIOPIIDAE 



e a First antennae with 2 flagella, posterior periopods very broad. 



2. PONTOPOBEIIDAE 



d, First antennae usually longer than second, or of nearly the same length. 

 e t Secondary flagellum present ; both pairs of gnathopods usually of 



same size 5. GAMMABIDAE 



e, Secondary flagellum usually absent; second pair of gnathopods 



larger than the first 6. PHOTIDAE 



c a Last pair of pleopods end in a hook 7. AMPHITHOIDAE 



5, Body flattened, with small abdomen 8. COROPHIIDAE 



o. Last 3 abdominal somites fused with caudal stylets 9. CHELUEIDAE 



FAMILY 1. OBCHESTIIDAE. 



The beach fleas. First antennae much shorter than the second; 

 mandible without palp; body laterally compressed; second gnathopod 

 much larger than the first: about 13 genera and 100 species, which live 

 largely on the seashore and are more or less adapted to a terrestrial life. 



Key to the genera of Orchestiidae here described: 



! First antennae shorter than peduncle (long basal segments) of second. 

 &! Dark-colored animals found on the seabeach 1. ORCHESTIA 



6, Whitish animals which burrow in the sand 2. TALORCHESTIA 



a, First antennae longer than peduncle of second 3. HYALELLA 



