456 Ommatogammarus, Odontogammarus 



the hind margin at the narrowed distal end not forming a free angle. Uropod 1 

 reaching end of inner ramus of uropod 3. Uropod 3, outer ramus broad, about 

 twice as long as the naiTow inner one, 2'^ Joint indistinct. Colour yellow 

 to clear honey-yellow. L. 30 mm. 



Lake Baikal. Depth 100—1300 m. 



i3. O. carneolus (Dyb.) 1874 Gammanis c, B. Dybowsky in: Horae Soc. ent. 

 E,oss., i'. 10 suppl. p. 73 I 1899 Ommatogammarus c, T. Stebbing in: Tr. Linn. Soc. 

 London, ser. 2 v.7 p.427 j 1893 Gammarus fluviatilis (part.)?, A. DellaValle in: F.FI. 

 Neapel, v. 20 p. 928. 



Dorsal spines of pleon segments 4 — 6 arranged as in 0. amethystinus. 

 Eyes large, unique in form, like the capital letter B reversed, with 2 great 

 lobes in front, the hinder and lower margins being also broken up into lobes, 

 ruby-red. Anteuna 1 more than V2 ^s long as body, nearly twice as long as 

 antenna 2, peduncle shorter than peduucle of antenna 2, flagdlum 3 or 4 times as 

 long as peduncle, 31 — 45-jointed, accessory flagellum 4- or 5-jointed. Antenna 2, 

 flagellum 11 — 1 5-jointed, peduncle and flagellum closely beset with simple 

 setae, which are sometimes longer than the flagellum itself. Gnathopod 1, 

 6*^ Joint slender, piriform; gnathopod 2, 6*'^ Joint oblong; in both gnatho- 

 pods pretty closely covered with setae often exceeding the length of the 

 Joint. Uropod 1 not reaching the middle of uropod 3. Uropod 8, outer ramus 

 about twice as long as inner. Colour flesh-red, variable in intensity. L. 18 mm. 



Lake Baikal. Depth 300—700 m. 



4. O. amethystinus (Dyb.) 1874 Gammarus a., B. Dybowsky in: Horae Soc. 

 eut. Ross., ?;. 10 suppl. p. 74 t. 9 f. 6 j 1899 Ommatogammarus a., T. Stebbing in: Tr. 

 Linn. Soc. London, ser. 2 v. 7 p. 427 | 1893 Gammarus fluviatilis (part.)?, A. Della Yalle 

 in: F. Fl. Neapel, 'v. 20 p. 927. 



Dorsal spines veiy delicate, 1 or 2 on the obscure elevations of the 

 hind margins of pleon segments 4 and 5, corresponding to middle and lateral 

 groups, Segment 6 having only 2 spinules. Dorsal line of head slightly convex, 

 rostral point depressed. Eyes small, narrow, hind margin broken up into 

 lobes, reddish or bright rose-red to whitish red. Antenna 1 % — % ^^ 1^^8' ^^ body, 

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

 flagellum 3 or 4 times as long as peduncle, 35 — 62-jointed. accessory flagellum 4- 

 or 5-jointed. Antenna 2, ultimate and penultimate joints of peduncle subequal, 

 flagellum 12 — 16-jointed. Gnathopod 1, 6*^^ Joint sleuderly piriform, the 

 concave palm forming a sinuous line with the hind margin. Gnathopod 2, 

 5**^ Joint decidedly longer than that of gnathopod 1, 6*^ evenly oblong, shorter 

 than that of gnathopod 1, but scarcely narrower than its widest part. Peraeo- 

 pods 3 — 5, 2'^ Joint with convex hind margin produced below to a rather long 

 obtusely ending process. Uropod 1 reaching middle of uropod 3. Uropod 3, 

 outer ramus about twice as long as inner, its 2^ Joint distinct. (Jolour amethystine 

 to bluish red. L. 24 mm. 



Lake Baikal. Depth 500—1300 m. 



42. Gen. Odontogammarus Stebb. 



1899 Odontogammarus, T. Stebbing in: Tr. Linn. Soc. London, ser. 2 «7.7 p.427. 



In general like Gammarus (p. 460). Lower front angle of side-plate 5 

 forming a tooth. Peduncle of antenna 1 not shorter than peduncle of antenna 2, 

 3^ Joint as long as 2'^. Gnathopod 1, 6*^ Joint not smaller than that of 



