Ommatogammarus 455 



1. O. albinus (Dyb.) 1874 Gammarus a., B. Dybowsky in: Horae Soc. ent. 

 Ross., u 10 suppl. p. 71 t. 9 f . 3 I 1899 Ommatogammarus a., T. Stebbing in: Tr. Linn. 

 Soc. London, ser. 2 i'. 7 p. 427 | 1893 Gammarus fluviatilis (part.)?, A. DellaValle in: 

 F. El. Neapel, v. 20 p. 927. 



Dorsal spines on pleon segments 4 — 6 very delicate, and solitary 

 at the places corresponding to lateral gi'oups. Head abruptly bent down- 

 ward, the dorsal line being connected by a short curve with a frontal 

 part at right angles to it. Eyes deep, closely adjoining tbe upright fi-out 

 of head, front margiu slightly concave (Fig. 86), liinder cut into very unequal 

 lobes, some of which are acute, clear flesh-coloured or white with a dash of rose- 

 red. Antenna 1 (Fig. 86) about ^^ as long as body and twice as long as antenna 2, 

 peduncle rather shorter (or in o sometimes a . ^ „ 



f., ,, 1 N ,, j 1 '^e 4. o Accessory flagellum 



little longer) than peduncle oi antenna 2, 

 P* Joint thick, longer than 2^ and 3^ combined, 

 flagellum 3 or 4 times as long as the short 

 peduncle^ 38-jointed, accessory flagellum 6 — 8- 

 jointed. Antenna 2 (Fig. 86), ultimate and pen- 

 ultimate joints of peduncle subequal, flagellum 



10-13-jointed. Gnathopod 1, 6*^ Joint piri- Head, antenna^e /and'2. 



form, very broad at base, bind margin much [After b. Dybowsky.] 



shorter than the veiy oblique but well defined 



palm. Gnathopod 2, 5*^ and 6*^ joints longer and more slender than 

 in gnathopod 1, 6*^^ Joint oblong, but gradually widening to the oblique 

 palm, which is shorter than bind margin. Peraeopods 3 — 5, 2^ Joint with 

 convex hiud margin but narrowed near the distal end, where it forras a 

 free angle. Uropods 1 and 2 reaching the second third of uropod 3. üropod 3, 

 outer ramus about twice as long as inner, 2* Joint distinct. Colour more or less 

 yellowish white. L. 28 mm. 



Lake Baikal. Depth 300- 1300 m. 



2. O. flavus (Dj'b.) 1874 Gammarus f., B. Dybowsky in : Horae Soc. ent. Ross., 

 u 10 suppl. p. 72 t. 9 f . 1 I 1899 Ommatogammarus f., T. Stebbing in: Tr. Linn. Soc. 

 London, ser. 2 v.l p. 427 j 1893 Gammarus fluviatilis (part.)?, A. Della Valle in: F. Fl. 

 Neapel, ».20 p. 928. 



Dorsal spines very delicate, on pleon segments 4 and 5 in 4 little gi'oups, 

 on Segment 6 only in 2, spines in a group varyiog between 1 and 3. Head bent 

 at right angles as in 0. albinus, but the connectiug curve larger. Pleon 

 segments 2 and 3, postero-lateral corners acutely produced. Eyes veiy large, 

 occupying nearly half the surface of head and nearly meeting at top, front 

 margin closely adjoining upright front of head, bind margiu divided into 

 sraall rounded lobes, lowersfcraightora little concave, blackor, in specimensfrom 

 a gi-eat depth, reddish. Antenna 1 about 7» ^s long as Body, in d less, in g more, 

 than twice as long as antenna 2, peduncle shorter than peduncle of antenna 2 

 (or in 9 sometimes a little longer), flagellum 3 or 4 times as long as peduncle, 

 35 — 43-jbinted, accessory flagellum 4- or 5-jointed. Antenna 2, ultimate and 

 penultimate joints of peduncle subequal, flagellum 13— 19-jointed. Gnathopod 1, 

 6**1 Joint described as slenderly piriform, but rather oblong, the bind margin 

 being considerably louger than the oblique, very concave palm, which is 

 armed with a strong spine at the centre. Gnathopod 2, 5**^ Joint rather longer 

 than in gnathopod 1, 6*^ oblong, considerably shorter but nearly as broad 

 as in gnathopod 1, bind margin slightly indented near the short, concave, 

 nearly transverse palm. Peraeopods 3 — 5, 2*^ Joint narrower than in 0. albinus, 



