348 GAMMARIM. 



A MP HIP OB A . GA MM A RIDES. 



NATATORIA. 



Genus MCERA. 



Mara. Leach, Eclin. Encyc. vii. p. 403. Linn. Trans, xi. 



p. 359. Samouelle, Ent. Comp. p. 103. Desma- 

 rest, Consicl. sur Crust, p. 246. Spence Bate, Cat. 

 Amph. Brit. Mus. p. 187 (not Dana). 



Leptothoe. Stimpson, Mar. Invert, of Grand Manan, p. 46. 



Gammarus (pars). Milne Edwards, Hist. Crust, iii. p. 49. 



Generic character. Animal long and slender. Superior 

 antennae much longer than the inferior, having a secondary 

 appendage. Coxae not so deep as their respective segments. 

 Second pair of gnathopoda larger than the first. Pereiopoda 

 subequal. Posterior pair of pleopoda biramous. Rami equal. 

 Telson double. 



The species forming this genus are long, and not 

 very robust. The eyes are normal ; and the antennae are 

 long ; those of the superior pair have the peduncle con- 

 siderably longer than the nagellum, while the inferior 

 pair of antennae seldom exceed the length of the 

 peduncle of the superior. The oral appendages some- 

 what recede from the facial line ; and the mandibles are 

 furnished with a tri-articulate appendage. All the legs 

 have the coxae less deep than the segments to which they 

 respectively belong. The hands of the first two pairs of 

 legs are subchelate ; those of the first pair being small, 

 while those of the second are large. The thighs of the 

 last three pairs are not much dilated. The last pair of 

 caudal appendages are biramous, and the branches are 

 of equal length. The terminal tail-piece is double. 



