A.STACUS. L39 



as A. pullipcs (=A.j;tir,';;/{* Hell), and not A. M.W////.V Kndi ( A. lm nlnnn 

 Schrank). 



A careful treatise by Kessler* on the Astact found within the- territory 

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

 forms, Kessler, in opposition to Gerstfeldt, decides that ,1. jlnmilH'^ Atict., 

 A. pachypus Eathke (= A. Caspius Eichwald), and A. /V///w/^-////^ Ksdisdioltz, 

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

 A. Icptodaciijlus 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 different 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 ]SMi l>v 

 Klunzinger,f who confirms Lereboullet in his conclusion that there are two 

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

 Russia. To Lereboullet's A. kngwornis he restores the older name of Sdirank, 

 A. torrenlium (= A. saxatilis, fristis, and torrcit/lnw of Koch). The distinctions 

 between this species and A. pallipes, or the Dohlenkrebs of Lereboullet, arc 

 given in detail, and the identity of the latter with A. xu.nt/ili* of Heller, the 

 Steinkrebs from the Rhone of Gerstfeldt, and probably with A.fonl!nalis of 

 Carbonnier, is pointed out. 



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

 A. fluviatilis Rond., A. torrent htm (Schrank), A. leptoihtetyhts Eschsch. (with var. 

 itiigitlosits), A. puchypus Rathke, A. pallipes Lereb., and A. Cokhicus Kes-1. 



In Astacus fluviatilis there are three rudimentary pleurobranchiae on each 

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

 while in A. pallipes there are but tw-o, the anterior one being aborted. In 

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

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



* Die Russiseheu Flusskrebse. Vorlaufige Mittlicilung. Bull. Soc. Iiuper. Nat. Moscou, XI, VIII. 



31:5-372, 1874. 



t Ueber die Astacus-Artcii in Mittcl- und Siulcurop.i uml il'ii Lcrchniilln'^-lirii Dohlenkrebs insbc- 

 sondero. Jahreshcfte d. Vereius f. vatcrliiudische Naturkuiidc in Wurttemberg, XXXVIII. Jalirg., i';>. 326- 

 342, 1882. 



J Counting the antennulary somite as the lirst. 



The difference in the number of rudimentary pleurobvanchiic in A.jluciatilis and A. pallipes was first 

 noticed by Huxley, The Crayfish, p. 295, 1S80. 



