Odontogammarus 457 



gnathopod 2. Peraeopods 3 — 5, 2^ Joint produced at lower bind angle into 

 a tooth. Uropod 3 not very long, the 2-jointed outer ramus (as in Gammarus) 

 longer tlian the inner. 



2 species. 



Synopsis of species: 



In side-plate 5 the tooth bent slightly outward. ... 1. O. calearatua . . . p. 457 

 In side-plate 5 the tooth directed straight downward . 2. O. margaritaceus . p. 457 



1. O. calcaratus (Dyb.) 1874 Gammarus c, U. Dybowsky in: Horae Soc. ent. 

 ßoss., 17.10 suppl. p. 54 t. 7 f. 4 | 1893 G. c. (part.), A. DellaYalle in: F. Fl. Neapel, 

 17.20 p. 759 I 1899 Odontogammarus c, T. Stebbing in: Tr. Linn. Soc. London, ser. 2 

 V.7 p.427. 



Pleon Segments 4 and 5 each with 3 little groups of dorsal spines 

 on hind margin, segment 6 with 2 little groups, 2 or 3 spines to a group. 

 Side-plate 5 in front half produced far down in a tootb-like angle, bent 

 slightly outward from the body, the hind angle little prominent so that to 

 the rear the lower margin forms almost a straight line; side-plate 6 in front 

 half produced over 2'* Joint of peraeopod 4, slightly pointed, not forming a 

 tooth; side-plate 7 rounded in front. Eyes small, reniform, black. Antenna 1 

 rather more than '/o ^.s long as body and twice as long as antenna 2, peduncle 

 as long as or a little longer than peduncle of antenna 2, 1^* Joint scarcely 

 longer and 2*^ perhaps a little shorter than 3'^'. flagellum twice as long a» 

 peduncle, 45 — 62-jointed, accessory flagellum 8 — 10-jointed. Antenna 2, 

 ultiraate Joint of peduncle longer than penultimate, flagellum shorter than 

 peduncle, 22-joiuted, with calceoli in ö. Characters of gnathopods 1 and 2, 

 6*^^ Joint diftering in text and flgure. Peraeopods 3 and 4, 2'^ Joint with front 

 margin very convex, much more so than in peraeopod 5, in all the bind 

 margin is slightly concave, ending below with a long tootb-like angle, 

 reaching far over the 3*^ Joint (wanting in young from the brood pouch), 

 üropod 1 reaching nearly to the middle of uropod 3. Uropod 3, 2^ Joint 

 of outer ramus about V? of 1^* Joint, inner ramus "/^ as long as outer, 

 both with plumose setae on both margins. Colour dorsally greenish yellow,^ 

 iridescent, on sides dark yellow, here also nacreous. L. 36 mm (including 

 6 mm for uropod 3). 



Lake Baikal. Depth 50—100 m. 



2. O. margaritaceus (Dyb.) 1874 Gammarus m., ß. Dybowsky in: Horae 

 Soc. ent. Ross., vAQ snppl. p. 21, 56 | 1899 Odontogammarus m., T. Stebbing in: Tr.^ 

 Linn. Soc. London, ser. 2 v.l p.427 | 1893 Gammarus calcaratus (part.)?, A. DellaValle 

 in: F. Fl. Neapel, v. 20 p. 929. 



Like 0. calcaratus, but head more convex 'and in front more obtuse; 

 side-plate 5 deeper, with front and hind angles nearly equally long, runuing 

 out into triangulär pointed lappets, of which the front one is somewhat the 

 sharper and longer; side-plate 6, with front corner rounded, hind one produced 

 acutely downward. Eyes irregularly linear-reniform, with broken hind margin^ 

 white, scarcely or not at all visible in spirit. Antenna 1, flagellum 53 — 63-jointedy 

 accessory flagellum 7-jointed; antenna 2, flagellum 19— 27-jointed. Peraeo- 

 pods 3 — 5, 2^ Joint broader, with hind corner more weakly developed. üropod 3 

 shorter, but inner ramus relatively longer, outer margin of outer ramus without 

 plumose setae and its 2*^ Joint diminutive. Colour bright yellowish playing 

 into bluish. 



Lake Baikal. Depth 150—1000 m. 



