ASTACUS. 159 
as A. pallipes (= A. furiaiils Bell), and not A. savatilis Koch (= A. torrentinm 
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, pachypus Rathke (= A. Caspius Eichwald), and A. leptodactylus Eschscholtz, 
are good species, while he considers A. aigulosus to be a local variety of 
A. 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. fuwiatilis in that part of Europe which lies to the west of 
Russia. To Lereboullet’s A. Zongicoriis he restores the older name of Schrank, 
A. torrentium (= A. saxatilis, 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. swratilis of Heller, the 
Steinkrebs from the Rhone of Gerstfeldt, and probably with A. fouinalis of 
Carbonnier, is pointed out. 
The twelve nominal species enumerated above are thus reduced to six: 
A. fluviatilis Rond., A. torrentium (Schrank), A. /eptodactylus Eschsch. (with var. 
angulosus), A, pachypus Rathke, A. pallipes Lereb., and A. Colchicus Kessl. 
In Astacus fluviatilis there are three rudimentary pleurobranchizw on each 
side of the body, upon the tenth, eleventh, and twelfth body-segments, ¢ 
while in 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 branchie of 
* Die Russischen Flusskrebse. Vorlaufige Mittheilung. Bull. Soc. Impér. Nat. Moscou, XLVI. 
343-372, 1874. 
+ Ueber die Astacus-Arten in Mittel- und Siideuropa und den Lereboullet’schen Dohlenkrebs insbe- 
sondere. Jahreshefte d. Vereins f. vaterlandische Naturkunde in Wirttemberg, XX XVIII. Jahrg., pp. 326- 
342, 1882. 
+ Counting the antennulary somite as the first. 
§ The difference in the number of rudimentary pleurobranchie in 4. fluviatilis and 4. pallipes was first 
noticed by Huxley, The Crayfish, p. 295, 1880. 
