764 PROF. T. H. HUXLEY ON THE CLASSIFICATION [June 4, 



podobranchia is devoid of even a trace of a lamina ; in the five which 

 precede it, on the other hand, the lamina is very large, and folded 

 into two longitudinally plaited lobes, as in Astacus. The edges and 

 the surfaces of the laminae present tubercles, which are more pro- 

 minent than in Astacus, and bear similar hooked spines. 



The inner decurrent prolongation of the lamina is wider than in 

 Astacus, particularly in the anterior podobranchiee. It is also beset 

 with hooked setae mounted on low tubercles. 



The setae of the upper part of the base are relatively shorter. 

 As in Astacus, their apices are straight and not hooked. 



The coxopodites bear bundles of twisted setae, which are similar 

 to those of Astacus, but are more obtusely pointed. 



The arthrobranchiae are similar in number and in form to those of 

 Astacus. Those of the posterior series are proportionately larger. 



I cannot discover a trace of the hindermost pleurobranchia, nor of 

 the rudiments of the anterior ones, in this species ; but it is not im- 

 probable that they may be discovered in larger forms. 



The modified podobranchia (epipodite) of the first maxillipede is 

 soft, and folded longitudinally in such a manner as to present a broad 

 and shallow anterior groove. It bears no branchial papillae, nor any 

 setae ; but there are a few short hooks here and there. 



The Branchial formula of Cambarus. 



Somites „ , Arthrobranchiae. „, 



and their , Pod °: , - % ^ a ^ 



appendages. brauchi*. Anterior. Posterior branch,*, 



VII (ep) 0=0 (ep) 



VIII 1 1 0=2 



IX 1 1 1 0=3 



X 1 I 1 0=3 



XI 1 1 1 0=3 



XII 1 ] I 0=3 



XIII 1 I 1 0=3 



XIV 0=0 



(J + ep + 6 + . 5 + = 17 -f ep. 

 In comparison with Astacus, there is obviously a reduction of the 

 branchial system, arising from the complete disappearance of all the 

 pleurobranchiae in Cambarus. 



3. The Branchice of Astacopsis ' franklinii. 



When the branchiostegiie is removed, seven branchiae are seen, 

 having the general appearance and disposition of those of Astacus ; 

 and, as in Astacus, the six anterior are podobranchia?, attached to the 

 coxopodite of the second maxillipede and the five following append- 

 ages, while the seventh is a pleurobranchia, fixed to the epimeron of 



1 Since, as will be shown below, those Australian Crayfishes winch neither 

 belong to Champs nor to En g mis are distinct from Astacoidcs, as represented 

 by the Madagascar species, I propose to apply the generic name of Astacopsis 

 to them. 



