470 Gammarus 



9 . Body sleuder and compressed, pleon segments 4 and 5 eacli with 

 a median fascicle of 2 — 4 spinules and 2 lateral groups of 3 spiuules. segment 6 

 with a pair of spinules. Head, lateral lobes broad, vertically truneated. Side- 

 plates 1 — 4 without setao, l"^^ little expanded distally, but broader tban 2*^. 

 4^^ rather ))road. Pleon segments 2 and 3, postero-lateral corners quadrate. 

 Eyes sraall, oval reuiform. Antenua 1 slender, more tban half as long as body. 

 1^* Joint not as long as 2^ and 3*^ combined, flagellum twice as long as 

 peduncle, 20-jointed, accessory flagellum 4-jointed. Antenna 2 scarcely more 

 than half as long as antenna 1. Gnathopod 1, 5^^ Joint short, 6*'' large, oblong 

 oval, palm oblique but well defined. Gnathopod 2 slender. 5^'' and 6^^ joints 

 subequal, long, sublinear, palm small, almost transverse, the 6^'' Joint beiug 

 shorter and very much narrower than in gnathopod 1, but ')^^ and 6*'^ joints 

 together longer tlian the same two in gnathopod 1. Peraeopods 1 and 2 

 rather slender. Peraeopods 3 — 5, 2<^ Joint rather broad and expanded, with 

 free corner to liind margin in peraeopod 4 as well as 3 and 5. in peraeopod 5 

 much larger, with the expansion obtusely truneated below. l'ropod 3 extending 

 much beyond the others, outer ramus long, sublinear, with fascicles of spines 

 on each margin, 2*^ Joint small, spiniform, inner ramus scale-like, shorter 

 than the short peduncle. Telson broader than long, lobes rather divergent, 

 each with 1 lateral spine and 3 spinules on the obtuse apex. L. 5 mm. — 

 ö unknown. 



Caspian Sea. 



18. G. ischnus Stebb. 1896 G. tenellus (non. .1. D. Dana 1852!), G. 0. Sars in: 

 J3ull. Ac. St.-Fetersb., ser. 5 (•.4 p. 455 t. 7 f. 12—24 \ 1899 G. ischnvs, T. Stebbing in: 

 Tr. Lina. Soc. London, ser. 2 v. 7 p. 428. 



Body exceedingly slender and compressed, pleon segments 4 — Ü each with 

 1 median and 2 lateral fascicles of slender, upturned spinules, usually 2 to 

 a group, sometimes together with a setule. Head, lateral lobes very obliquely 

 ti'uncated, upper angle acutely prominent. Side-plates 1 — 4 not large, quite 

 smooth, pt scarcely expanded, distally rounded, 4*'' not very broad. Pleon 

 segment 2, postero-lateral corners acutely quadrate, in segment 3 acutely 

 produced. Eyes well developed. but rather small, oblong oval, close to 

 margin of head. Antenna 1 more than half as long as body. peduncle long, 

 1^* Joint not as long as 2^ and 3*^ combined, flagellum twice as long as 

 peduncle, 20-jointed, accessory flagellum 4-jointed. Antenna 2 considerably 

 shorter. setose, especially in ö, ultimate and penultimate joints of peduncle 

 equal, flagellum 11-jointed. Gnathopods 1 and 2 rather feeble in o, stronger 

 in ö, not very unequal. but gnathopod 2 the longer, 6^'' Joint oblong, with 

 palm rather oblique in gnathopod 1 and in d somewhat concave, in gnathopod 2 

 nearly transverse. Peraeopods 1 and 2 rather slender, much smaller than 

 the others. Peraeopods 3 — 5. 2*^ Joint narrowly oval, in peraeopod 5 scarcely 

 difteiing from that in 4^^^. not forming a free corner in any peraeopod. üropods 1 

 and 2, outer ramus rather shorter than inner, l'ropod 3 very long, out«r 

 ramus sublinear, with 5 fascicles of spines on each side. 2*^ Joint spiniform, 

 well defined, tipped with setules, inner ramus scale-like, shorter than the 

 short peduncle. Telson small, much broader than long, lobes divergent, 

 with 2 spinules on outer margin of wide upper part, thence rapidly tapering 

 to obtuse apex with 3 spinules. L. 9 6 mm, ö a little longer. 



Caspian Sea (sonth of Baku). Uepth 11 m. 



19. G. placidus O. Sars 1896 G. p. (O. Grimm in MS.), G. O. Sars in: Bull. 

 Ac. St.-Petersb., ser. 5 v.4 p. 457 t. 8 f. 1—12. 



