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Show 1878.] AND DISTRIBUTION OF THE CRAYFISHES. 771 The branchia? of two specimens of a Paranephrops, from the Fiji Islands, like the foregoing in the British Museum, are in such bad condition, the specimens having apparently got dry before they were placed in spirits, that I cannot make out all the details of their structure ; but, so far as it can be ascertained, they agree with those of the preceding species. 7. The Branchice of Parastacus. By the kindness of Prof. Peters, I have been able to examine two well preserved males of the Astacus brasiliensis and A. pilimanus of Von Martens; and the results are very interesting. The branchiae of the two species are so much alike that they may be described together. In many points they resemble those of Chceraps; but the structure is by no means identical ; and as these Crayfishes are peculiar in other respects, I think it will be most convenient to consider them as members of a distinct genus, Parastacus. There are six ordinary podobranchia?, of which, as usual, the first is the smallest, the next two are longer, and the last three are longest of all and nearly equal. In the podobranchia of the second maxillipede, the inner lip of the groove of the stem of the branchia is produced into a broad ala, as in Chceraps ; but the ala becomes broader towards the apex, and is there abruptly truncated. The truncated edge is fringed by a single series of branchial papilla?. The posterior lip of the groove is beset with long hooked setae. In the four following podobranchia? the ala is a little narrower, especially at its apex, but it has essentially the same characters. In the last the ala is present in the basal half of the stem, but narrows to a mere ridge in the apical half. The modified podobranchia of the first maxillipede bears from ten to sixteen longer or shorter branchial filaments on the outer half of the posterior surface of its apical end (fig. 2, D, p. 759). The six anterior arthrobranchiae are full-sized, and increase in length from before backwards. The five posterior arthrobranchiae are much smaller; and the last is rudimentary, consisting of a very short slender stem, with from one to three lateral filaments. There are four pleurobranchiae, all well developed, but the hinder-most the longest. In the podobranchia?, many of the posterior branchial filaments are terminated by hooks. As usual, these are absent in the other branchiae. The coxopoditic tubercles give origin to bundles of long and tortuous setae, with hooked apices. These are neither so long, nor so numerous, as in Astacus and Cambarus, but are more like them than are those of any other Parastacidee. |
