416 Hakonboeckia, Baikalogammarus 



witb mid hind margiu u little thickened and raised over following segmeut. 

 Head, upper profile arched witli rosti-um projectiug helm-like aiid deflexed; 

 linder part of cheek-lobes strongly projectiug outward and runuiug down into 

 a free acute point. Eyes very prominent, large, oval, dark hrown. Antenna 1 

 little more tlian V^ «»s long «s body, about twice as long as antenna 2, peduncle 

 stouter tban that of antenna 2 but equal in leugth. flagellum 9- or 10-jointed, 

 accessory flagellum 2-jointed. Gnathopods 1 and 2. 6^^^ Joint oblong, widening 

 a little to the not very oblique palm, larger in gnathopod 1. Peraeopods 3 — 5, 

 2'^ Joint broad, heart-sbaped, bind margin witb 3 or 4 short spine-like setae. 

 Uropod 1 not reacbing the end of uropod 3. Uropod 3 '/g as long as body, 

 rarai subequal, outer witb plumose setae only on inner margin, inner ramus 

 liaving tbcm on l>oth margins. Colour dark grey or dark green brown, antennae 

 brigbt, under part of body and peraeopods dark blue or dark violet; a variety 

 brigbtly coloured, side-plates and under body dark blue. L. 10—11 mm. 



Lake Baikal. Depth 20—100 m. 



26. Gen. Baikalogammarus Stebb. 



1899 Baikalogammarus (Sp. typ.: B. pullus), T. Stebbingiii: 'J'r. Linn. Soc. London, 

 ser. 2 V. 7 p. 42;"). 



Neär to Gammarus (p. 460). Pleon segments 4 — 6 witb a few dorsal 

 setules or spinules. Antenna 1 tbe longer, peduncle shorter tban peduncle 

 of antenna 2, accessory flagellum very sbort. Gnathopod 1, 6^'' Joint not smaller 

 tban 6*^ Joint of gnathopod 2. Peraeopods 3 — 5, 2*^ Joint broad, the wing 

 produced downward in a long rounded lobe. Uropod 3 ratber elongate, 

 witb peduncle as long as the 2-jointed outer ramus. Telson cleft. 



1 species. 



1. B. pullus (Dyb.) 1874 Gammarus p., B. Dybowsky in: Horae Soc. ent. Ross., 

 ?;. 10 suppl. p. 170 t. 11 f. 4 i 1893 Atylus? ]>., A. Della Valle in: F. Fl. Neapel, «.20 

 p. 930 I 1899 Baikalogammarns p., T.Stebbing in: Tr. Linn. Soc. London, ser. 2 v.7 p. 425. 



Pleon Segments from 2*^, 3* or 4"' to the 6*11 with 2 — 4 dorsal setules 

 or very line spines. Head, rosti'um slightly deflexed and forming a helm- 

 like promiuence, post-antenual corn«rs (in tigure) rounded. Side-plates 1 — 4 

 witb isolated short setae. Eyes large, widened above, black. Antenna 1 

 about ^/g as long as body, a little longer tban antenna 2, 1^^ Joint stout, not 

 as long as 2*Mind 3'^combined, flagellum 15- 18-jointed, accessory flagellum 

 1-jointed. Antenna 2, ultimate Joint of peduncle longer tban penultimate, 

 curved, flagellum 7 — 10-jointed. Gnathopod 1, 6^^ Joint described as piriform, 

 but in flguro oblorg oval, widening a little to the oblique palm which is 

 ratber shorter tban the hind margin. Gnathopod 2. 6^^^ Joint oblong, ratber 

 smaller tban in gnathopod 1. Uropod 1 reacbing end of uropod 3. Uropod 2 

 only reacbing end of peduncle of uropod 3. Uropod 3 ^/^ (less?) of lengtb 

 of body; peduncle as long as outer ramus, which has 2^ Joint nearly V3 as 

 long as P*; inner ramus -/.j as long as outer; both with plumose setae on 

 inner margin. Telson in flgure very small, much shoiiier tban peduncle of 

 m-opod 3. Colom- gi-een, spotted with brown. L. 9 6, d 8 — 9 mm (including 

 uropod 3). 



Lake Baikal. Depth 3 — 10 m. 



