56 



THE VOYAGE OF H.M.S. CHALLENGES. 



Group NORMALIA. 



This group consists of those Trichobranehiate Macrura in which the branchiae are well 

 developed, and the pleon does not preponderate in importance over the carapace. 



It consists of three tribes, that present j>eculiarly distinctive features, illustrated in 

 their external form, their structural character, and development, as shown in the subjoined 

 table : — 



3 



o 



Tribe Synaxidea. 



Branchiae well developed, having mastigobranchial plates attached to all the pereio- 

 poda except the posterior pair. Podobranchia attached to all the mastigobranchise as 

 distinct plumes. Arthrobranchiae attached to the joints of all the pereiopoda, and 

 pleurobranchiae to the walls of the four posterior somites of the pereion. First pair of 

 antennae terminating in two flagella. Second pair without any scaphocerite. Pereiopoda 

 six-jointed, having no perfect chela. First pair of pereiopoda, but little larger than the 



