428 EEV. T. E. R. STEBBINa ON AMPHIPODA TKOM 



DiKEROGAMMARUS, n. g. 



Pourth and fifth pleon-segments each raised dorsally to a spiniferous tuhercle. First 

 antennae the louger; accessory flagellum well developed. The gnathopods larger in the 

 male than in the female ; the second larger than the first. The form agrees in general 

 with Gmmnarus. 



The generic name alludes to the two horn-like elevations on the pleon. 



The species included are : — Bilierogmnmurus macrocephalus (Sars), 1896 ; 2. D. hcemo- 

 baphes (Eichwald), 1842 ; 3. B. Grimmi (Sars), 1896 ; 4. B. Verreauxii (Bate), 1862 ; 

 5. D.fasciatus (Say), 1818. The first three are found in the Caspian, the fifth in streams 

 and ponds of the United States of America. The fourth is said to have been found by 

 M. Verreaux in New Holland, Spence Bate ascribing the species to " Edwards, Ann. des 

 Sc. Nat.," a vague reference which has not yet been verified. 



Gen. Gammaeus J. C. Fabricius, 1775. 



For Gammarus tenellus Sars, 1896, which is distinct from Gammarus tenellus Dana, 

 1852, I propose the equivalent name G. ischims. For G. marimis Risso, 1826, which is 

 distinct from G. viarinus Leach, 1815, it is useless to propose a wqw name while the 

 species remains unidentilied. 



PffiKILOGAMMARUS, U. g. 



All segments of perseon and pleon usually having dorsal hairs or spinules. Head 

 rostrate. First antenme with peduncle longer tlian that of the second pair, its tliird 

 joint longer than the second. Upper lip with wide, almost straight, apical margin. 

 Under lip, as in AccelboecMa, having the principal lobes separated by what may be rudi- 

 mentary inner lobes. First maxillae with about six sette on the inner plate. Outer 

 plate of maxillipeds not reaching far along the second joint of the j)alp. Hand of first 

 gnathopods larger than that of second. Third uropods with equal i-ami, both carrying 

 plumose setae ; outer ramus one-jointed. General character like Gammarus. 



The generic name alludes to the variegated colouring of the several species. 



The species included are : — Pcekilogammariis pictus (Dybowsky), 1874 ; 2. F. orchestes 

 (Dybowsky), 1874; 3. P. talUnts (Dybowsky), 1874; 4. P. araneolus (Dybowsky), 

 1874 ; all from Lake Baikal. 



ECHINOGAMMARUS, n. g. 



In general like Gammarus, but with dorsal spines on segments anterior to the fourth 

 of the pleon ; the first antennae longer than the second, though with shorter peduncle ; 

 the hand of the first gnathopods almost always larger than that of the second. 



The generic name alludes to the numerous spines on the body. 



