366 CRUSTACEA 



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

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

 jeMMsh; coast of New- England, north of Cape 



cJf 



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). n , i r-r 



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 1,000 species. 



Key to the families of Gammaridea here described : 



Oj Three last abdominal somites normal and not fused together. 

 hx Body compressed and not flattened. 

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

 dx First antennae usually shorter than second. 

 Cx First antennae without secondary flagellum. 

 fx First antennae much shorter than the second. 



Qx Two eyes present .* 1. Orciiestiidae 



Qi Four eyes present 3. Ampeliscidae 



^2 First antennae but little shorter than second 4. Calliopiidae 



ej First antennae with 2 flagella, posterior periopods very broad. 



2. PONTOPOREIIDAE 



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

 Cx Secondary flagellum present ; both pairs of gnathopods usually of 



same size 5. Gammaridae 



62 Secondary flagellum usually absent ; second pair of gnathopods 



larger than the first 6. Photidae 



Ca Last pair of pleopods end in a hook 7. Amphithoidae 



fta Body flattened, with small abdomen 8. Corophiidae ^ 



C3 Last 3 abdominal somites fused with caudal stylets 9. Cheluridae 



Family 1. OKCHESTIIDAE. 



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



mandible without palp; body laterally compressed; second gnathopod 



much larger than the firsdujibout 13 genera and 100 species, which live 



largely on the seashore ancBt-e more or less adapted to a terrestrial life. 



Key to the genera of OrcJiest{idae here described : 

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



bx Dark-colored animals found on the seabeach 1. Orchestia 



6j Whitish animals which burrow in the sand 2. Talorchestia 



Oj First antennae longer than peduncle of second 3. Hyalella 



