S66 
GAMMA R1DJE. 
AMP HIP OB A. GA MM A RIDES. 
NATATORTA. 
Genus— GAMMARUS. 
Gammarus. Fabricius, Ent. Sjst. ii. p. 514. Latreille, Hist. Nat. des 
Crust., &c. vi. p. 315. Gen. Ins. i. p. 58. Leach, Edin. 
Encyc. Art. Crustaceology, vii. p. 404. Trans. Linn. Soc. 
xi. p. 359. Lamarck, Hist, des Anim. sans Yert. v. 179. 
Desmarest, Consid. sur les Crust, p. 265. Milne Ed- 
wards, Ann. des Sci. Nat. xx. p. 366. Hist, des Crust, iii. 
p. 42. (Division 1. A. a.) Kroyer, Gron. Amph. p. 27. 
Rathke, Fauna der Krym. p. 372. and Nova Acta Leop. 
1843. Samouelle, Ent. Comp. p. 103. White, Hist. Brit. 
Crust, p. 182. Gosse, Mar. Zool. i. p. 141. Liljeboro, 
(Division + 1. 6.) Ofvers. af Kongl. Yet. Akad. Forliandl. 
1853, p. 446. Bruzelius (Division a a — !>.), Skand. 
Amph. Gamm. p. 50. Spence Bate, Cat. Amph. Brit. Mus. 
p. 204. 
Astacus pars. Pennant, Brit. Zool. iv. p. 21. 
Generic character. Three posterior segments of the pleon 
furnished with fasciculi of spines on the dorsal surface. Eyes 
linear or reniform. Antennae slender, filiform ; superior fur- 
nished with a secondary appendage. Mandibles having an 
appendage. Gnathopoda subequal ; Propoda not much dilated. 
Posterior pair of pleopoda biramous. Telson double. 
In this genus the body of the animal is laterally com- 
pressed, so much so that the animal has not the power of 
walking upright when out of the water. The head is 
not produced into a rostrum ; and rarely, if ever, is the 
hack carinated. Each of the last three segments of the 
tail has one or two small fasciculi of spines. The eyes 
are linear or reniform. The antennae are long, slender, 
and filiform, the superior pair being furnished with a 
secondary appendage. The mandibles are furnished with 
a triarticulate appendage. The first two pairs of legs 
are not much dilated, and have the hands of nearly the 
same size. The remaining legs are nearly of uniform 
length ; but the coxae of the last three pairs are very 
