A.STAOUS. 139 



as A. pallipes (= A. fluviatilis Bell), and not A. sazcdilis Koch (= A. torrentium 

 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. fluviatilis Auct., 

 A. paehypus Eathke (= A. Caspius Eichwald), and A. kptodaetylus Eschscholtz, 

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

 .1. leptodactylus 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 1882 by 

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

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

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

 A. torrentium (==A. s'axatilis, tristis, and torrentium of Koch). The distinctions 

 between this species and A. pallipes, 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. fluviatilis Komi., A.torrentium (Schrank), A. leptodactylus Eschsch. (with var. 

 angulosus), A. pachypus Rathke, A. pallipes Lereb., and A. Oolchicus Kessl. 



In Astacus fluviatilis there are three rudimentary pleurobranchiae on each 

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

 while m A. pallipes 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 branchiae of 



* Die liussisclieu Flusskrebse. Vorliiufigc Mittheilung. Bull. Soc. Imp6r. Nat. Moscou, XLVIII. 

 343-372, In" I. 



I ii I- die Lstacus-Arteu in Mittel- und Siideuropa und dm Lereboullet'schen Dohlenkrebs insbe- 

 sondere. Jahreshefte d. Vereins f. vaterlaudische Naturkunde in Wurttemberg, XXXVIII. Jalirg., pp. 326- 

 342, 13S2. 



% Counting the antennularj somite as the Srst. 



§ The difference in the iber of rudimentary pleurobranchiae in A.fuviatilis and A. pallipes was first 



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



