52 G. 0. SAKS. [X. S. IT 



It is thus a very considerable bulk of Caspian Crustacea, that will lie 

 before me, and I hope that a careful investigation of this vast material will 

 prove to be of considerable interest, both in systematic and biological 

 respects, and that several fundamental conclusions relating to the early 

 history of the Caspian Sea may be hence derived. I think, however, it may 

 be convenient to delay such a general discussion until the completion of 

 the systematic investigation of the several groups. On this occasion I only 

 wish quite briefly to indicate the general suggestions to which a preliminaiy 

 examination of the specimens has led me, and which I hope subsequently 

 to be enabled to support by more reliable facts. 



The fauna of the Caspian Sea is, I believe, derived from 3 very differ- 

 ent sources. One part is of true arctic origin, and constitutes the remuaut 

 of the primitive fauna prevailiog at the early time, when a connexion between 

 the Caspian Sea and the Polar Sea may have existed. Another part of the 

 fauna is of a more southern character, and may have immigrated, at a much 

 later period from the Black Sea and the Mediterranean; a direct connexion 

 being supposed to have existed at that time. A third part of the fauna, 

 finally, constitutes a number of true fresh-water forms, which have adapted 

 themselves to living in somewhat brakish water, at the estuaries of the 

 great rivers debouching in the Caspian Sea. The abyssal region of the Cas- 

 pian Sea remains still, I believe, nearly quite unexplored. I am, however, 

 much inclined to believe that, on a closer investigation, the great depths of 

 that basin will be found to contain a peculiar abyssal fauna exhibiting a 

 purely arctic character. 



On entering upon an investigation of the carcinological fauna of the 

 Caspian Sea, I have thought it right to treat of each group separately. The 

 present part comprises only a single family of the Schizopoda, viz., the Jly- 

 sMcs. It will be shortly succeeded by 2 other parts, the one treating of the 

 Cumacea, the other of the Amphipoda, and perhaps subsequently a 4th part 

 will be added, treating of the lower Crustacea, the Entomostraca. 



31 YS ID^. 



As is well known, the Mysidce form a family of the lower stalk-eyed 

 Crustacea, and belong to the subdivision generally termed Schizopoda, on 

 account of the legs being biramous, or provided with greatly developed exo- 

 podites acting as powerful swimming organs. Of higher stalk-eyed Crusta- 

 cea only 2 species of the genus Astacus have hitherto, according to a kind 

 communication by Mr. Herzenstein, been recorded from the Caspian Sea, 

 viz., Astacus leptodactylus and A. pachypus, both being evidently fresh- 



Me'langes biologiqncs. T. XIH, p. 400. 



