Carinogammarus 503 



front and concave hind margin; ou pleon segments 4 — 6 becoming hump- 

 like and gradually weaker; marginal swelliugs are perceptible on the peraeon- 

 segments and pleon segments 1 — 4, and on either side of the median carina in 

 pleon segments 4 — 6 are strong humps, carrying 2 or 3 spinules each. Head, 

 rostral point short. Side-plates 1—4 rather deep, 5*^ not deep. Eyes slightly 

 prominent, reniform, black. Antenna 1 about % as long as body, more 

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

 and longer tban the 70-jointed flagellum, accessory flagellum 11— 13-jointed, 

 longer than the 12-jointed flagellum of antenna 2. Gnathopods 1 and 2, 

 6*^ Joint rather large, piriform, tinger long. Peraeopods 3— 5, 2^ Joint heart- 

 shaped, longitudinally carinate (in figure). üropod 3 reaching back much beyond 

 the others, the rami subequal, long, not foliaceous, both with numerous plumose 

 setae and (in figure) with short stout spiues, 2*^ Joint of outer ramus rudimentary. 

 Colour bright yellow, with delicate markiug. L. 46 mm. 



Lake Baikul. Depth 70—150 m. 



3. C. pulchellus (Dyb.) 1874 Gammarus p., B. Dybowsky in: Horae Soc. ent. 

 Ross., u 10 suppl. p. 118 t. 5 f. 4 I 1899 Carinogammarus p.. T. Stebbing in: Tr. Lina. 

 Soc. London, ser. 2 v.7 p. 429 | 1893 Gammarus fluviatilis (pari.)?, A. DellaYalle in: 

 F. Fi. Neapel, v. 20 p. 930. 



Peraeon segment 7 and segments of pleon with a low median carina, 

 which is obscurely developed on pleon segment 6; surface of body with delicate 

 hairs on the bind pai't of the segments. Head with a small subacute rostrum. 

 Side-plates 1 — 4 rather deep, with numerous setules on lower margin, 4*^^ broad, 

 well emarginate behind; pleon segment 3, postero-lateral corners quadrate. 

 Eyes rose-red, so placed on lateral lobes as to show partly in front between 

 antennae 1 and 2, halfmoon-shaped, convex margin in front, bind margin 

 irregulär, cut into lobes. Antenna 1 about ^a '<^^ long as body, nearly 

 twice as long as antenna 2, P' Joint thick, flagellum with 20—29 rather 

 long joiuts, accessory flagellum with 3 or 4. Antenna 2, flagellum H — 9-jointed. 

 Mandible, 3^ Joint of palp curved, much shorter than 2'^. Gnathopods 1 and 2 

 small, slender, 5^^ Joint rather long, especially in gnathopod 2, 6*^ Joint 

 oblong, with palm oblique in gnathopod 1, but transverse in gnathopod 2, 

 the Joint being also slightly widened at the palm, finger short. Peraeopod 3, 

 2^ Joint nearly circular. Peraeopods 4 and 5, 2*^ Joint wide, with a distal 

 uarrowing, many spinules and setae on the expanded part. üropod 1 is 

 Said to reach as far back as üropod 3, or in 5 somewhat farther. üropod 3, 

 inner ramus longer than 1^* Joint of outer, both beset with spines and plumose 

 setae, 2*^ Joint of outer about % as long as 1^*. Telson with a few setules 

 on the obtuse but narrow apices of the tapering lobes. Colour very delicately 

 reddish white. L. reaching 23 mm. 



Lake Baikal. Depth 100—700 m. 



4. C. seidlitzii (Dyb.) 1874 Gammarus s., B. Dybowsky in: Horae Soc. ent. 

 ßoss., i;. 10 suppl, p. 119 t. 5 f. 5 | 1899 Carinogammarus s., T. Stebbing in: Tr. Linn. 

 Soc. London, ser. 2 v.7 p. 429 | 1893 Gammarus fluviatilis (part.)?, A. Della Valle in: 

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



Peraeon segments 6 and 7 and pleon segments 1 — 3 with a weak median 

 carina forming a tubercle at about the middle of the segments; the spinules 

 on the 5*^ and 6*^ pleon segments are extremely delicate; head, peraeon, and 

 pleon segments 1 — ^3 dorsally beset with delicate hairs, longest on hind 

 margin of peraeon segments. Head narrow, rostrum subacute, not large. Side- 

 plates 1 — 4 with long setae on lower margin. P]yes moderately large, not very 



