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Show 768 PROF. T. H. HUXLEY ON THE CLASSIFICATION [June 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 setae in the position of the bundles of long coiled coxopoditic setae of Astacus and Cambarus (fig. 5, vi). Somites and their appendages. VII VIII IX X..... XI XII XIII XIV The Branchial formula of Astacopsis Arthrobranchise. Podobranchia}. Anterior. 0 (ep r) 0 1 1 1 1 1 1 1 1 1 1 1 1 0 0 Posterior. 0 0 1 1 1 1 1 0 Pleurobranchia;. 0 = 0 = 0 = 0 = 1 = 1 = 1 = 0 (ep r) 2 3 3 4 4 4 1 6 + ep r+6 + 5 + 4 = 21+ep r. 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 pleurobranchiee: only the hindermost podobranchia, the first and last anterior arthrobranchiae, the first two and the last posterior arthrobranchiae, and the first four pleurobranchia? 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 Branchiee of 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 Museum1. 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 decurrent 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 terminated 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 M y best thanks are due to Dr. Giinther, F.E.S., for the readiness with which he has aided m y investigations by giving m e free access to the Crusta-fcan collection under his charge. |
