366 GAMMA R1D.E. 



A MPHIP ODA. GA MM A RIDES. 



NATATORTA. 



Genus— GAMMARUS. 



Oammarus. Fabricius, Ent. Syst. 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 Vert. v. 179. 

 Desmarest, Consid. sur les Crust, p. 265. Milne Ed- 

 wards, Ann. des Sei. Nat. xx. p. 366. Hist, des Crust, iii. 

 p. 42. (Division 1. A. a.) Kkoter, 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. Liljeborg, 

 (Division + 1- ^•) Of vers, af Kongl. Vet. Akad. Forliandl. 

 1853, p.- 446. Bruzelius (Division aa — b.), 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 doi'sal surface. Eyes 

 linear or reuiform. Antennfe 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 

 back 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 



