510 Acanthogammarus 



than inner, both with numerous plumose setae. Telson divided. Colour 

 rose-red or violet, with yellowish shimmer above. L. 32 mm. 

 Lake Baikal. Depth 300—700 m. 



3. A. godlewskii (Dyb.) 1874 Gammarus g. -\- G. g. var. victorii, B. Dybowsky 

 in: Horae Soc. ent. Ross., v. 10 suppl. p. 143, 144 t. 1 f. 6 | 1893 Ceradocus? g., A. Della 

 Valle in: F. Fl. Neapel, t?. 20 p. 928 | 1899 Acanthogammarus g.. T. Stebbing in: Tr. 

 Linn. Soc. London, ser. 2 u 7 p. 430. 



Median carina usually on peraeon segmeuts 1 — 4 forming short, blunt 

 teeth, on peraeon segments 5—7 and pleon Segments 1 — 3 long, acute teeth, 

 those on peraeon segment 7 and pleon segment 1 the longest, on pleon segment 

 4 a Short, blunt tooth; on pleon segments 5 and 6 the carina is weak, 

 not dentate; the coalesced marginal and lateral carinae on peraeon segments 

 1 — 3 represented by short teeth standing out horizontally from the body and 

 directed somewhat backward; on segment 4 the tooth is of unique size, (especially 

 in var. victorii)-, on segments 5 — 7 the teeth are short; on pleon segments 

 1 — 4 giving place to fiat swellings, and on segments 5 and 6 unrepresented. 

 Head rough above, with a depression at the front, rostrum short, acute. 

 Side-plates 1—4 with concave lower margin, 1^* produced acutely forward, 

 2*^ and 3*^ rather narrowed distally; 4*^^ pentagonal, much deeper than 5*^ 

 with lateral projecting spine-like tooth near lower margin. Eyes prominent, 

 reniform, black. Antenna 1 longer than half the body, more than twice as long as 

 antenna 2, peduncle thicker and longer than that of antenna 2, or in variety 

 more slender and shorter, 3*^ Joint in d as long as 1^*, or rather longer, 

 flagellum 50 — 60-jointed, accessory flagellum 10-jointed. Antenna 2, ante- 

 penultimate Joint of peduncle in ö cylindric, in 9 flattened and about 5 times 

 as long as broad, flagellum 11-jointed. Gnathopods 1 and 2, 6^^ Joint piriform, 

 in gnathopod 2 bind margin more convex than in gnathopod 1. Peraeopods 

 3 — 5, 2*^ Joint narrow, longitudinally carinate; in peraeopods 3 and 4 the 

 bind margin slightly sinuous, in 5*^ slightly convex, in all fringed with 

 Short, simple setae. üropod 1 reaching beyond uropod 3. Uropod 3, inner 

 ramus little shorter than outer, both with numerous plumose setae. Telson 

 divided to the centre, or (in the variety) more deeply. Colour reddish or 

 brownish yellow. L. reaching 76 mm. 



Lake Baikal. Depth 10 — 150 m. 



4. A. radoszkowskii (Dyb.) 1874 Gammarus r., ß. Dybowsky in: Horae Soc. 

 ent. Ross., t'. 10 suppl. p. 149 t. 13 f. 3 | 1893 Ceradocus ? r., A. Della Valle in: F.Fl. 

 Neapel, u 20 p. 930 | 1899 Acanthogammarus r., T. Stebbing in: Tr. Linn. Soc. London, 

 ser. 2 ». 7 p. 430. 



Median carina on peraeon segments 1 — 7 and pleon segments 1 — 3 

 tubercular, on pleon segments 4 and 5 forming a streng, broad tooth, with 

 humps on the front surface, on pleon segment 6 reduced to a feeble elevation; 

 lateral carinae on peraeon segments 1 — 7 and pleon segments 1 — 3 consisting of 

 little humps, successively smaller; marginal carinae represented by feeble 

 swellings, those on pleon segments 4 and 5 each caiTying 2 or 3 spine-points. 

 Head, upper surface level, rostrum very short, much less advanced than the sub- 

 quadrate lateral lobes. Side-plate 1 slightly 'expanded below and directed 

 forward, 4*^ broad, convex in front and below, behind produced outward into a large 

 semicylindrical blunt tooth. Pleon segments 2 and 3 (in figure), postero-lateral 

 Corners quadrate. Eyes small, offen point-like, irregulär in shape, white. 

 Antenna 1 scarcely '/s ^-s long as body, about twice as long as antenna 2, 

 peduncle not thicker but shorter than peduncle of antenna 2, flagellum 



