Zoology.'] NATURAL HISTORY OF VICTORIA. lOrustacea. 



The two Cray-fisli, A. serratus and A. hicarinatus^ which I have 

 figured in this work, differ from the Madagascar genus, Astacoides, 

 to which I, with all the best continental writers, had referred them, 

 in the larger number of the gills (Astacopsis having twenty- 

 one and a rudiment, Astacoides only twelve fully developed). 

 Placing A. serratus in the genus Astacopsis, which Professor 

 Huxley has proposed, and which is entirely peculiar to Austraha, 

 the A. hicarinatus may be referred to a" section of Astacopsis 

 forming the sub-genus Chceraps of Erickson (if he be assumed to 

 be wrong in saying the fifth legs have no gills), as, in our speci- 

 mens, the gills in number, structure, and position are, as Huxley 

 pointed out, like Astacopsis., but the podobranchias diflfering in 

 having the inner anterior edge of the stem widened into an ala, 

 covered with branchial filaments. 



The old family, AstacidcB., is divided from Professor Huxley's 

 observation into two groups, one inhabiting the Northern Hemi- 

 sphere, for which the name Potamobiidce has been suggested, 

 including the genera Astacus and Camhai-us, in which the gUls 

 from the first joint, or coxfe, of the five thoracic legs on each side 

 have the upper part of the stem dilated posterioi-ly into a broad 

 double, plaited lamina, and that of the adjacent jaw-foot is reduced 

 to an epipodite without branchial filaments, none of the branchial 

 filaments or setfe ending in hooks ; the first abdominal segment 

 always with appendages in the male, or in both sexes ; those of the 

 four following joints small ; the telson, or middle piece of the tail- 

 fin, divided transversely by a more or less perfect joint. 



The second group, named Parastacidce, confined to the Southern 

 Hemisphere, containing the genera Astacoides, Astacopsis, ChcBvaps, 

 EngiBus, and Parastacus, is distinguished by the absence of the 

 upper posterior laminae to the podobranchiae : having branchial 

 filaments on the epipodite of the hind jaw-foot. The filaments of 

 the podobranchiaj mostly end in hooked spines, as well as the 

 setsB at their base and stems ; the telson is not divided by a trans- 

 verse sutm-e ; the first abdominal segment has no appendages in 

 either sex, and those of the four following segments are large. 



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