ASTACUS. 139 



as A. pallipcs [^ A. fiuviaiilis Bell), and not A. saxatilis Koch (t= A. turrentium 

 Schrank). 



A careful treatise by Kessler* on the Astaci found within the territory 

 of the Russian Empire appeared in 1874. With regard to the European 

 forms, Kessler, in opposition to Gerstfeldt, decides that A. flumaiilis Auct., 

 A. pach>/pus Eathke (= A. Caspius Eichwald), and A. leptodadylm Eschscholtz, 

 are good species, while he considers A. anguloms to be a local variety of 

 A. Icptodadjjlm which has arisen in the stony mountain streams of the Crimea 

 and Caucasus. Kessler has had unrivalled facilities for forming a correct 

 judgment concerning the specific value of the different forms of Russian 

 crayfishes, hundreds of specimens of both sexes and of diflerent stages of 

 development having passed through his hands. His direct testimony as to 

 the absence of intermediate forms between the three species indicated above 

 appears to me conclusive, and a careful study of all the material accessible 

 leads me to coincide entirely with his views. 



The Astaci of Middle and Southern Europe were revised in 1882 by 

 Klunziny:er,t who coiifirms Lereboullet in his conclusion that there are two 

 species besides A. flimatilis in that part of Europe which lies to the west of 

 Russia. To Lereboullet's A. longicornls he restores the older name of Schrank, 

 A. ton-eullniH (:=/!. saxatilis, trisiis, and iorrcniium of Koch). The distinctions 

 between this species and A. pallipcs, or the Dohlenkrebs of Lereboullet, are 

 given in detail, and the identity of the latter with A. saxatilis of Heller, the 

 Steinkrebs from the Rhone of Gerstfeldt, and probably with A. fontinalis of 

 Carbonnier, is pointed out. 



The twelve nominal species enumerated above are thus reduced to six : 

 A. fliaiatilis Rond., A. torrentiwn (Schrank), A. hptodadi/lus Eschsch. (with var. 

 angulosus), A. puchgpus Rathke, A. pallipes Lereb., and A. Golchicus Kessl. 



lu Astacus fluviatitis there are three rudimentary pleurobranchias on each 

 side of the body, upon the tenth, eleventh, and twelfth body-segments, t 

 \i\\\\Q m A. pallipcs there are but two, the anterior one being aborted. § In 

 the place of the anterior one a small papilla can be discerned, evidently the 

 last vestige of the lost branchia. I have further examined the branchiaj of 



* Die Russisclieu Flusskrebse. Vorlaufige Mittlieilung. Bull. Snc. Imper. Nat. Moscoii, XLVIII. 

 313-372, 1874. 



f Ueber die Astacus-Artcn in Mittel- und Siideuropa und den LerebouUet'sclien Dohlenkrebs insbe- 

 soudero. Jahresliefte d. Ycrcius f. vaterlaudische Kaliirkimde in Wiirttemberg, XXXVIII. Jahrg., pp. 326- 

 342, 1882. 



X Counting tlie antennulary somite as the first. 



§ The dill'erence in the number of rudimentary plcurobrancliise in A.JIuviatilis and A. paltipes was first 

 noticed by Huxley, The Crayfish, p. 295, 1880. 



