1878.] AND DISTRIBUTION OF THE CRAYFISHES. 7/1 



The branchiae of two specimens of a Paratiephrops, 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 Astaeus 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 

 Lharaps ; 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, Par- 

 astacus. 



There are six ordinary podobranchiae, 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 

 maxilhpede, the inner lip of the groove of the stem of the branchia 

 is produced into a broad ala, as in Ghceraps ; 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 

 tour following podobranchiae 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 maxilhpede 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 podobranchiaa, 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 Astaeus and Cambarus, but are more like them 

 than are those of any other Parastacidce. 



