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Show 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 prominent than in Astacus, and bear similar hooked spines. The inner decurrent prolongation of the lamina is wider than in Astacus, particularly in the anterior podobranchiae. It is also beset with hooked setae mounted on low tubercles. The seta; 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 improbable 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 and their appendages. VII VIIIXI X XI XII XIII XIV. Podobranchiae. 0(ep 1 1 1 1 1 1 0 Arthrobranchiae. Anterior. ) o 1 1 I 1 ] I 0 Posterior 0 0 1 1 1 I 1 0 Pleuro-branchise 0 0 0 0 0 0 0 0 = = = = = = - 0(ep) 2 3 3 3 3 3 0 6 + ep + 6 4- 5 + 0 = 17 + 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 Branchiee of Astacopsis' franklinii. W h e n the branchiostegite is removed, seven branchiae are seen, having the general appearance and disposition of those of Astacus; and, as in Astacus, the six anterior are podobranchiae, attached to the coxopodite of the second maxillipede and the five following appendages, while the seventh is a pleurobranchia, fixed to the epimeron of 1 Since, as will be shown below, those Australian Crayfishes which neither belong to Chceraps nor to Engceus are distinct from Astacoides, as represented by the Madagascar species, I propose to apply the generic name of Astacopsis to them. |