Heterogammarus, Parapallasea 497 



as antenna 2, peduncle stouter and a little longer than peduncle of antenna 2, 

 flagellum 24- — 29-joiuted, accessory flagellum 3-jomted. Antenna 2, ultimate 

 Joint of peduncle shorter than penultimate, flagellum 5- or 6-jointed. Gnatho- 

 pods 1 and 2 in (5, 6*'^ Joint piriform. Gnathopod 1 in 9, 6*** Joint piriform; 

 gnathopod 2, 6*^ Joint oblong. Peraeopods 3 — 5, 2^ Joint tolerably broad, 

 in peraeopod 5 scarcely ^/^ longer than broad. the wing below forming a free, 

 often lobe-like corner. üropod 1 reaching end of uropod 3. üropod 3 

 about Vii ^s long as body, outer ramus with 2 spines and 2 simple setae 

 on outer margiu, plumose setae on inner; inner ramus very little shorter, with 

 plumose setae on both margins. Colour dark brown, with cross-bands of 

 brighter spots on head and mid-peraeon. L. about 12 mm. 



Lake Baikal. . Depth '/j — 2 m, uiider stones. 



8. H. branehialis (Dyb.) 1874 Gammariis b., B. Djbowsky in: Horae Soc. 

 ent. Ross., v. 10 suppl. p. 110 t. 14 f. 4 | 1899 Heterogammarus b., T. Stebbing in: Tr. 

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

 in: F. FI. Neapel, u20 p. 927. 



Pleon Segments 1 — 3 with a few fine dorsal setae, segments 4 — 6 each 

 with 2 regulär groups of 2 or 3 spines. Head, rostrum a short rounded 

 point. Side-plates 1-4 setiferous. Eyes rather large, oval, narrowed below, 

 jalack. Antenna 1 about ^/^ as long as body, more than twice as long as 

 antenna 2, peduncle stouter but little longer than peduncle of antenna 2, 

 flagellum 15 — 17-jointed, accessory flagellum 2-jointed. Antenna 2, ultimate 

 Joint of peduncle shorter than penultimate, flagellum 4- or 5-jointed. Gnatho- 

 pods 1 and 2, 6*^ Joint nearly equal, piriform. Peraeopods 3 — 5, 2^ Joint 

 tolerably broad, alike in the 3 pairs, bind margin more convex than front, with 

 widely separated setae, but these often in ö wanting on peraeopod 5. Uropods 1 

 and 2 nearly reaching end of uropod 3. üropod 3 ^/j, — Y^g as long as 

 body, outer ramus with 3 — 5 fascicles of simple setae on outer margin, 

 3 pairs of setae on inner; inner ramus about half as long as outer, with 

 3 pairs of long setae on inner margin. Colour changing with that of the 

 host. L. 9 — 14 mm. 



Lake Baikal. Only taken in marsnpium of larger Gammarids, or among the 

 branchiae of the males. 



48. Gen. Parapallasea Stebb. 



1899 Parapallasea, T. Stebbing in: Tr. Linn, Soc. London, ser. 2 v.7 p. 429. 



Median carina not represented on peraeon or on pleon segments 1 — 3. 

 Side-plate 4 broader, but not less deep than the preceding, emarginate behind. 

 Antenna 1, flagellum longer than peduncle, accessory flagellum elongate. 

 Peraeopods 3 — 5 with 2*^ Joint little expanded. Telson deeply cleft. Other 

 characters agreeing with Pallasea (p. 374). 



3 species. 



Synopsis of species: 



J Median carina present on pleon segments 4 — 6 ... 1. P. borow^skii . p. 498 

 \ Median carina wanting — 2. 



f Lateral carinae chiefly composed of tooth-likeprocesses 2. P. lagowskii . p. 498 

 \ Lateral carinae chiefly composed of wing-like processes 3. P. puzyllii . . p. 498 

 Das Tierreich. 21. Lief.: T. R. ß. Stebbing, Amphipoda I. 32 



