236 



GAMMA RID^. 



AMPHIPODA. 



NATATORIA. 



OAMMARIDES. 



Genus— DEX AMINE. 



Dexamlne. Leach, Edin. Encyc. vii. p. 433. Spekce Bate, Cat. 



Amph. Brit. Mus. p. 130. 

 Acanthonotus (pars). Milne-Edwaeds, Ilist. des Crust, iii. p. 25. 



Generic character. Superior antennae having the third joint 

 of the peduncle reduced in size, so as to resemble the first 

 articulus of the flagellum ; without a secondary appendage. 

 Mandibles having no^ appendage. Gnathopoda feeble, subclie- 

 late. Telson single, divided. 



In this genus the antennae are of moderate length, slen- 

 der, and nearly of corresponding proportions ; both pairs 

 are remarkable for the absence of a joint in the pe- 

 duncle ; but this absence is pi'obably more apparent than 

 real, arising from the last joint in each being reduced to 

 the form and appearance of the articuli of the flagellum. 

 The mandibles are not furnished with an appendage, a 

 peculiarity especially characteristic of the Orchestid^. 

 The first two pairs of legs are subchelate, although 

 slender. The coxae of the four anterior pairs of legs 

 are subequally deep and rounded ; those of the three 

 posterior are scarcely more than half as deep as the 

 preceding. The posterior pair of caudal appendages 

 are two-branched, and the central terminal plate is 

 single, but constantly divided to a considerable extent 

 down the middle. 



This genus was founded by Dr. Leach, to receive a 

 species described by Montagu under the name of Cancer 

 (Gammarus) spinosus, but it was not accepted by Prof. 

 Milne-Edwards, who referred Montagu's species to the 

 genus Acanthonotus. 



