140 A REVISION OF THE ASTACID^E. 



A. torrentium, A. Iqdodactylus, and A. Colchkus. The first of these possesses 

 two rudimentary pleurobranchiaj on each side of the body, like A. pulllpcs ; 

 of the anterior pleurobranchia I find not the slightest trace. In A. IqAodac- 

 tylus and A. Colchkus three are present, although in the former the second 

 and third are very short. 



In so far as the reduction of the brancliia3 can be taken as a clew to the 

 affinities of the various species of European Astaci, A. palUpes and A. torrcn- 

 timn are the furthest removed from the primitive form. This accords with 

 Huxley's suggestion, that the Ponto-Caspian species are the modern repre- 

 sentatives of the original Eastern stock, while the " Stone Crayfishes " * 

 represent an ancient offshoot, or western wave of migration, which was 

 followed by an invasion oi A. fluvkdUis, just as at the present day, according 

 to Kessler, the latter species is in its turn succumbing to A. Icptodudijlns in 

 the Baltic area.t Following up this line of thought, we must conclude that, 

 of the two species A. torrodkwi and A. pallipcf!, the former represents the 

 older offshoot from the original stock, an offshoot which has retreated before 

 the invading A. pallipes to the mountain regions of Central Europe. For not 

 only in the condition of its branchisB, but also in its general form, A. pallipes 

 stands between A. torrentium and A. fluviatilis. % 



In the European Astaci the first abdominal segment of the female carries 

 a pair of small, simple appendages. They are smaller than in the genus 

 Cambarus, but not aborted, § as in the American Astaci, in Cambaroides, and 

 in the Parastacinaa of the Southern hemisphere. 



In A. torreidmm and A. pallipes the first abdominal appendages of the 

 male are divided into two lobes at the tip by a shallow cleft, the inner and 

 the outer parts being of about equal length. In the other species the outer 

 part is truncate, while the inner part projects beyond it. In A. pachjpus and 

 A. Golchicus the projecting tip of the inner part is longer than in A. fluviatilis 

 and A. leptodactylus. 



The European Astaci, including A. Colchicus from the Rion River, Trans- 

 caucasia, may be distinguished by the following table : — 



* I. c. ^ pullipes aucl A. torrentium, whicli Huxley confounds togetlier as one species. 



f Vide Huxley, op. cit., p. 321. 



J Klunzingcr {op. cit., p. 381) goes so far as to assert tliat A. pallipes is more closely related to A.Jlu- 

 viatilis than to A. torrentium, but it does not seem so to me. A.Jluciatilis, A. leptodarti/lus (including the 

 form A. angulosus), A. pachypus, aud A. Colchicus form a natural group of closely related species opposed 

 to the group containing the two Western species, A. pallipes and A. torrentium. 



§ Huxley affirms, however, that these appendages are sometimes wanting in English crayfishes {^A. pal- 

 lipes). The Crayfish, p. U6. 



