Gammaracanthus 507 



51. Gen. Gammaracanthus Bäte 



1862 Gammaracanthus (part.), Bäte, Cat. Amphip. Erit. 3Ius., p. 201 | 1871 Gr., 

 A. Boeck in: Forh. Selsk. Christian., 1870 p. 214 | 1894 G., Q. O. Sars, Crust. Norway, 

 v.l p.493 I 1894 G., T. Stebbing in: Bijdr. Dierk., u 17 p.41. 



Body cariuate throughout, carina in many segments produced into 

 a tooth, lower margin of peraeon segments carinate, this carina continued 

 along middle of pleon segments 1 — 3 or 1 — 4. Head, rostrum long, acute, 

 lateral corners small, rounded, with prominent process below. Side-plates 

 1 — 4 ridged from above downward, parallel-sided, 5*'^ nearly as deep as 4*^, 

 its front lobe the deeper. p]yes ratber prominent, not veiy large. Antenna 1 

 witb accessory flagellum. Antenna 2 much sliorter, siender. Upper lip rounded. 

 Lower lip, inner lobes incompletely separated from outer. Mandible normal, 

 3*^ Joint of palp as long as 2'^. Maxilla 1. several (6) setae on inner plate, 

 11 spines on outer. Maxilla 2, inner margin fringed. Maxillipeds, palp 

 elongate. Gnathopods 1 and 2, 5*^ Joint sbort, cup-sbaped, 6^^' powerful, 

 finger long. Peraeopods 3 and 4 much longer tban 1**, 2*^ or b^^. Peraeopods 

 3 — 5, 2*1 Joint little expanded. üropod 1, rami shorter tban peduncle, equal. 

 üropod 3, rami longer tban peduncle, setose, laminar, ending obtusely. Telson 

 very small, bilobed. 



3 species. 



Synopsis of species: 



Pleon segments 2 and 3, postero-lateral corners quadrate 1. G. lacustris . . p.507 

 Pleon segments 2 and 3, postero-lateral corners acutely 

 produced — 2. 



Rostrum curved, produced beyond Ist Joint of antenna 1 2. G. loricatus . . p. 508 

 Rostrum almost straight, not produced beyond Ist joint 



of antenna 1 3. G. caspius . . p. 508 



1. G. lacustris 0. Sars 1861 Gammarus loricatus (en-., non Sabine 1821!), 

 S. Loven in: Öfv. Ak. Förh., u 18 p. 287 | 1867 Gammaracanthus l.var. lacustris, Gr. 

 O. Sars, Crust. d'Eau douce Norvfege, p. 73 t. 7 f. 1 - 8 ] 1888 G. lacustris, T. Stebbing 

 in: Rep. Voy. Challenger, u 29 p. 1699 j 1894 G. relictus, G. 0. Sars, Crust. Norway, 

 <;. 1 p. 494 t. 174 I 1896 G. r., G. 0. Sars in: Bull. Ac. St.-Petersb., ser. 5 v.i p. 439. 



Body siender and compressed, dorsal carina rather low in fi-ont, projections 

 scarcely beginning tili peraeon segment 5, tbose following to pleon segment 5 

 very acute. Head, rostrum very slightly curved, not reacbing end of 1®* Joint of 

 antenna 1, lateral corners very small, projection below tuberculiform. Pleon 

 segment 3, postero-lateral corners quadrate. Eyes rather small, rounded, 

 dark. Antenna 1 nearly V« ^^ ''^ng as body, 3*^ Joint not very sbort, 

 flagellum rather longer than peduncle, about 22-joitited, accessory flagellum 

 4-jointed. Antenna 2 little more than ^2 ^^ ^^^S ^^ antenna 1, basal 

 Joint tumid, ultiraate Joint of peduncle sborter tban penultiraate, flagellum 

 7-jointed. Gnathopod 1 fully as large as gnathopod 2, 5*^ Joint produced 

 to a small narrow setiferous lobe, 6*^ expanding to beginning of palm, wbich 

 is convex, scarcely longer than bind margin, defined by an obtuse angle and 

 several spines, one rather long. Gnatbopod 2, 6*^ Joint oblong oval, broadest 

 near tbe base, tapering distally, palm very oblique, much longer than bind 

 margin. Peraeopods 1 and 2 little longer than gnatbopods 1 and 2. Peraeopods 

 3 and 4 extremely 'siender and elongate, 5*^ Joint much longer than 4*^ 

 Peraeopod 5, 2'^ Joint a little more expanded proximally than in other peraeopods. 



