gammaridj:. 201 



tenna^ nearly hull' tlie length of the animal ; pt'dunclc as long as the 

 Hagellum ; secondary appendage short. Interior antenna) having 

 the peduncle a little shorter than the peduncle of the superior 

 antennae; flagellum scarcely longer than the last joint of the 

 pedimcle. Gnathopoda subecjual, having the coxa; as deep as the 

 pereion : first pair lunging the propodos tapering, palm obli(iue, 

 fringed with short equidistant hairs, and imperfectly defined by 

 several short blunt spines : second pair having the propodos 

 broader and less tapering, palm less obliqiie, fringed ■w'ith a 

 row of equidistant hairs, imperfectly defined by three stout blunt 

 spines ; inferior margin furnished Avith several fiisciculi of two 

 kinds of hail's — the one armed vrith short coarse denticular spines 

 on one side, the other with fine vertical hairs. First two pairs of 

 pereiopoda uniform ; coxae of the second pair furnished near the 

 centre with a prominent tubercle. Three posterior paii's of pereio- 

 poda having their basa ovate, dilated, and suddenly compressed. 

 Three posterior pairs of pleopoda having the rami free from hairs, 

 those of the penidtimate pair shorter than those of the preceding. 

 " Posterior pair not longer than the antepenultimate*." Telson 

 scarcely longer than broad, widely cleft at the apex. 

 Length li inch. 



Hub. Rivers of Siberia (Pallas et auct.). 



This species is very abundant, and is made use of by the inhabit- 

 ants of Siberia as a delicate article of food ; it is also devom-ed vora- 

 ciously by bii'ds. 



G4. GAMMARACANTHUS, n. g. 



Dorsal margin carinated, and ha\-ing the posterior central margin with 

 one or more segments produced posteriorly. I'leon without fas- 

 ciculi of spines. Superior antenna; having a secondaiy appendage. 

 Inferior antennae longer than the superior. Mandibles wath an 

 appendage. Maxillipeds subpediform, unguiculate, liaA'ing the 

 squamiform internal processes but slightly developed. Gnathopoda 

 subch elate and subequal, having the carpus inferiorly produced. 

 Coxa; of the third pair of pereiopoda not so deep as the foiu-th. 

 Posterior pair- of pleopoda bii'amous; rami foHaceous. Telson 

 double. 



This genus is selected from that of Gammarus of authors generally, 

 comprising the Division AA. of M.-Edwards, and + 1 a. of LUjeborg. 



» Edwards, /. r. The epecimcn from wliich this dcscriiJtion is taken has this 

 portion wanting. 



