\si vers, 151 



Sea and the Sea of Azov, and it is widely distributed in the Caspian Sea, 

 having been reported from the following points therein : Peninsula of Man- 

 ghishlak, Island of Cheleken, Krasnovodsk, Astrabad, Sara Island, Lenko- 

 ran, and Bakoo (Kessler, Eichwald). It has been taken with the dredge 

 from a depth of six to nineteen fathoms in the Caspian Sea (Kessler, p. 372). 

 1 have seen specimens from the basin of the Danube as far up as Balaton 

 Lake * in Hungary (Coll. Peabody Mus. Yale Coll.), and Heller reports it 

 from the Theiss River ami Mohacs. Middendorlf states that it ascends the 

 Volga system to the sixtieth parallel, in the neighborhood of Tcherdy.t 

 It is also found to the northward in the rivers and lakes which drain into 

 the Baltic and White Seas, Erichson reporting it from Courland,t Kessler 

 from many of the lakes and rivers that connect with the Gulf of Finland ; 

 viz. Lakes Ilmen and Valdai, and the rivers Vodla, Vytegra, Sveer, Volkhov, 

 and Msta.§ Here it has invaded the domain of A. flutriatilis, and according 

 to Kessler is supplanting that less fertile species.|| In the Northern Dwina 

 A. leptodactylw alone is found, descending to Archangel.** 



The Ponto-Caspian basin is undoubtedly the original home of A. leptodac- 

 lylns. Thence its migration into the northern rivers was made easy by the 

 canals connecting the Volga and Dnieper with the rivers of the Baltic and 

 White Seas. 



A. leplodacti/lus was introduced by man in 1822 into the River Isset, a 

 tributary of the Tobol, in Western Siberia, and is now common in many of 

 the streams of the Obi River basin, e. g. the Toora, Niza, Irtish, Tara, Ora, 

 and also in the upper part of the Obi. Its distribution over such a wide area 

 of the Obi basin is due partly to spontaneous spreading, partly to artificial 

 transference from one stream to another. It is probable that crayfishes did 

 not exist in the waters east of the Ural Mountains until they were trans- 

 ported thither by man, although Pallas ft speaks of their presence in the 

 upper course of the Ui, an affluent of the Tobol, as early as 1770. As the 



* Tlic water of Balaton Lake is said to bo slightly sail 



f Sibirisohe Eteise, Bd. IV. Th. 2, p. 882, ]s(J7. 



% Kessler {pp. <-it. p. 253 [353 ) doubts whether ./ leptodactylw be found in Courland, as Erichson 



annoi 'I ; bul as ill ■ Sum hern Dwina is connected b\ means of canals with both Lake Ilmen and tin- Bere 



ina River (an affluent of the Dnieper), immigration of this specie into I lourland would be facilitated. 



§ Tin- Msta, which Hows into Lake Ilmen, ami thence through Lake Ladoga into the Gulf of Finland, i» 

 i bj a canal with the TVertsa, a tributary '•!' the Volga. The Vytegra also communicates with the 

 i the Volga through the Murinskoi Canal. 



V ■ding to Kessler .-/. kptodaetylus lavs from 500 to 600 eggs, d.fluviatilti rarely more than 250. 



*" .-/. Ii-iit<iiliich/lti.i is also found in Lapland, according to Gerslfeldt, op. eit., p 589. 

 ff Reise duroh versohiedene Provinzen des Russischen Reiches, Th. 11. p. 381. 



