458 Dikerogammarus 



43. Gen. Dikerogammarus Stebb. 



1899 Dikerogammarus, T. Stebbing in: Tr. Linn. Soc. London, ser. 2 r. 7 p. 428. 



Agreeing in general with Gamraarus (p. 460). Pleon Segments 4 and 5 

 each raised dorsally to a spiniferous tubercle. Antenna 1 the louger, accessoiy 

 flagellum well developed. Gnathopods 1 and 2 larger in ö than in § , 

 2* larger than 1^*. 



5 spocies. 



Synopsis of species: 



J Uropod 3, rami very unequal — 2. 



\ Uropod 3, rami not very unequal — 4. 



j Head arched longitudinally I.D. macroceplialus . p. 458 



\ Head not arched longitudinally — 3. 



Peraeopods 3-5, 2d Joint broadly expanded . . 2. D. haemobaphes . . p. 458 

 Peraeopods 3 — 5, 2d joint not very broadly ex- 

 panded 3. D. grimmi p. 459 



j Gnathopod 2 much larger than gnathopod 1 . 4. D. verreauxii . . . p. 459 

 \ Gnathopod 2 not much larger than gnathopod 1 5. D. fasciatus .... p. 460 



1. D. macrocephalus (0. Sars) 1896 Gammarus m., G. O. Sars in: Bull. Ac. 

 St.-Petersb., ser. 5 ».4 j). 453 t. 7 f. 1 — 11 | 1899 Dikerogammarus m., T. Stebbing in: 

 Tr. Linn. Soc. London, ser. 2 ». 7 p. 428. 



Body robust, back smootbly rounded, except pleon segments 4 and 5, 

 tubercle of pleon segraent 4 tipped with 4, of segment 5 with 2 spines; 

 Segment 4 without lateral spines, segment 5 left doubtful, segment 6 with 

 2 on each side at base of telson. Head large, dorsal surface strougly vaulted, 

 with peculiar areolated appearance from points of Insertion of streng muscles 

 converging to the mouth area. Side-plates not particularly large. Pleon 

 segment 1, postero-lateral corners rounded, in segments 2 and 3 acutely 

 produced. Eyes very small. distinctly reniform. Antenna 1 slender, not 

 half as long as body, 1^* Joint as long as 2^ and 3*^ combined, flagellum 

 about 27-jointed, accessory flagellum 6-jointed. Antenna 2 stronger, rather 

 setose, flagellum 10-jointed. Gnathopods 1 and 2, 6*^ Joint oblong oval, 

 in gjiathopod 2 (at least in d) fully twice as large as in gnathopod 1, in 

 both palm oblique, well defined, rather shorter than bind margiu. Peraeo- 

 pods 1 — 5. rather slender, not very long. Peraeopods 3 and 4, 2 "^ Joint 

 wider above than below, bind margin siuuous. Peraeopod 5, 2"^ Joint much 

 larger, broadly oval, bind expansion produced below to an obtusely pointed 

 lobe. Uropods 1 and 2. rami subequal, not long, with apical groups of 

 spines. and here and there a lateral spine. Uropod 3 reaching far beyond 

 the others, peduncle short, outer ramus long, sublinear, fringed densely all 

 round with slender setae, and having 3 groups of spines on each margin, 

 2^ Joint minute; inner ramus little over ^a ^s long as peduncle. Telson 

 broader than long, each lobe having 3 spinules on narrowly truncate apex 

 L. d 24 mm. 



Caspian Sea. Depth 66 m. 



2. D. haemobaphes (Eichw.) ?1771 Oniscus pidex, Cancer p. (err., non Linne 

 1758!), Pallas, Reise Ruß., v.l p. 477 | 1841 Gammarus haemobaphes, Eichwald in: N. 

 Mem. Soc. Moscou, v.l p. 230 t. 37 f. 7a— c | 1899 Dikerogammarus h., T. Stebbing in: 

 Tr. Linn. Soc. London, ser. 2 v.l p.428 | 1894 Gammarus h. -}- G. robustoides {G. aralo- 



