478 Poekilogaiiimarus 



1. P. pietus (öyb.) 1874 Gammarus p. -f- Var. « -f- Var. ß, B. Dybowskv in: 

 Horae Soc. ent. Koss., ?). 10 suppl. p. lÜJi 1. 12 f. ;J; p. 104 1. 12 f.2(juv.) j 1899 Foekilo- 

 gammanis p., T.^tebbing in: Tr. Linn. Soc. London, ser. 2 v.7 p. 428 1893 Gamriianis 

 fhiviatilis (part.)?, A. DollaYalle in: F. Fl. Neapel, ?'. 20 p. 9130. 



Pleon Segments 4 — 6 with delicate dorsal spines. Head in front almost 

 straiglit, rostral point scarcely indicated. Eyes moderately large, very 

 prominent, as if set on tubereles, oval, black or brown. Antenna 1 longer 

 than Vo body (in young specimens longer than body), more than twice as long as 

 antenna 2, 2*^ Joint only about % as long as '.V^, flagellum 41 — 58-jointed, 

 accessory flagellum 6-jointed. Antenna 2, ultimate Joint of peduncie ratber 

 sborter than penultimate, flagellum 9 — ll-joiuted. Gnatliopods 1 and 2 

 little differing in size or even in shape, 6^^ Joint oblong, with palm more 

 oblique in gnathopod 1, bind margin longer in gnathopod 2, and 'the Joint 

 slightly widening to the palm, Peraeopods 3 — 5, 2^ Joint not very wide. 

 narrowing gradually from above downward, bind margin setose. üropod 1 

 reachiug end of uropod 3. Uropod 3 moderately long, the 1-jointed equal 

 rami fringed with plumose setae. Colour whitish yellow, variegated, with 

 brownish or greenish yellow markings. L. 32 mm. 



Lake Baikal. Deptli 50—100 m. 



2. P. orchestes (L)yb.) 1874 Gammarus o., B. Dybowsky iii: Horae Soc. eut. 

 Ross., ?;. 10 suppl. p. 104 | 1899 Poekilogammarus o., T. Stebbing- in: Tr. Linn. Soc. 

 London, ser. 2 v.7 p. 428 | 1898 Gammarus pietus (part.)?, A. DellaValle in: F.Fl. 

 Neapel, u 20 p. 929. 



Segments of peraeon each provided with 2 — 4 delicate setae; segments 

 of pleon completely covered with them. Head with middle dorsal line 

 convex, rostrum short, projecting with a slightly downward directed curve, 

 its apex obtuse. Eyes rather small, prominent, ovate, a little narrowed above. 

 black. Antenna 1 a little shorter than body, alraost twice as long as antenna 2, 2*^ 

 Joint about % shorter than 3*^, flagellum not twice as long as peduncie, 21-Jointed, 

 accessory flagellum 2-Jointed. Antenna 2, ultimate and penultimate Joints 

 of peduncie subequal, flagellum shorter than peduncie, 7-Jointed. Gnathopod 1, 

 6*^ Joint piriform. Gnathopod 2, 6**^ Joint oblong. Peraeopods 3 — 5. 2*^ Joint 

 slender, in front convex with long pendent setae, behind flatly coucave or 

 straight, with 5 or 6 setules. Uropods 1 and 2 scarcely reaching middle 

 of uropod 3. üropod 3 rather long, ^/^ — ^/^ as long as body. Colour yellow, 

 spotted with yellow ^ brown. L. about 10 mm. 



Lake Baikal. Depth 150 m. 



3. P. talitrus (Dyb.) 1874 Gammarus t., B. Dybowsky in: Horae Soc. ent. 

 Ross., u. 10 suppl. p. 105 1. 11 f. 5 I 1899 Poekilogammarus t., T. Stebbing in: Tr. Linn. 

 Soc. London, ser. 2 v.7 p. 428 | 1893 Gammarus pietus (part.)?, A. Della Valle in: 

 F. Fl. Neapel, r. 20 p. 930. 



Segments of peraeon each with 2 — 4 delicate setae; segments of pleon with 

 delicate, irregularly arranged setae on surface and bind margin. Head with 

 a rather long, straight, acute rostrum, downward bent only near the point. 

 Eyes moderately large, prominent, elongate oval, slightly narrowed below, not 

 far apart above, black. Antenna 1 about thrice as long as antenna 2, in d about 

 as long as body, in Q rather shorter, 2*^ Joint about ^ Z, shorter than 3*^, flagellum 

 more than twice as long as peduncie, 28 — 39-jointed, accessory flagellum 

 3 — 6-Jointed. Antenna 2, ultimate and penultimate joints of peduncie sub- 

 equal, flagellum shorter than peduncie, ll-Jointed. Gnathopod 1, 6*^ Joint 



