768 PROF. T. H. HUXLEY ON THE CLASSIFICATION [Julie 4, 



to a mere epipodite, but retains true branchial characters in the 

 scanty respiratory filaments of its outer lobe. 



There are only small tufts of short, straight or slightly curved seta? 

 in the position of the bundles of long coiled coxopoditic setae of 

 Astacus and Catnbarus (fig. 5, vi). 



The Branchial formula of Astacopsis. 



Thus Astacopsis presents a much nearer approximation to the 

 hypothetically complete branchial formula than Astacus, inasmuch 

 as the epipodite of the first maxillipede is an imperfect branchia, 

 and there are four complete pleurobranchiae : only the hindermost 

 podobranchia, the first and last anterior arthrobranchiae, the first 

 two and the last posterior arthrobranchiae, and the first four pleuro- 

 branchiae are wanting. In fact, this is the most complete branchial 

 formula with which I am at present acquainted, among the podo- 

 phthalmous Crustacea. 



4. The Branchia o/"Chseraps (?). 



I have examined a single specimen of a species attributed to this 

 genus, from the Yarra-Yarra river, in the collection of the British 

 Museum 1 . 



The second maxillipede and the five following thoracic limbs bear 

 podobranchiae, which increase in length from the first to the last, 

 and have a close general resemblance to those of Astacopsis ; but 

 they differ in the production of the upper part of the anterior lip of 

 the groove of the stem into a broad limb or ala, wider at the upper 

 end than below, which must not be confounded with the lamina of 

 Astacus, as it corresponds only with part of the inner lobe and the 

 decurreut fringe in that genus (fig. 6, i, n, in al). Both faces, 

 as well as the free posterior margin of this fringe, are beset with 

 cylindrical branchial filaments, the apex of each of which is termi- 

 nated by a strong sickle-shaped hook (fig. 6, iv). The majority of 

 the branchial filaments of the stem are also terminated either by 

 smaller hooks or by short straight spines. Long setae, hooked at 



1 My best thanks are due to Dr. Giinther, F.E.S., for the readiness with 

 which be has aided my investigations by giving me free access to the Crusta- 

 cean collection under his charge. 



