(XXXVI) | CRUSTACEA CASPIA. 53 
water forms, which have adapted themselses to living in somewhat bra- 
kish water. A species of Thelphusa is besides found in the rivers debouching 
into the southern part of the Caspian Sea, but this form cannot properly be 
referred to the fauna of the Caspian Sea itself. Unlike these 3 forms, the 
Myside are generally regarded as being of true marine origin, though 
some species are also occasionally met with in pure fresh water lakes, as 
first stated with regard to the Mysis relicta of Lovén. But, as indicated by the 
specific name, this species is believed to be left from a remote time, when 
the lakes were in connexion with the Ocean, and this view, set forth by 
Prof. Lovén, has been subsequently fully confirmed by a closer comparison 
with the marine form, Mysis oculata Fabr., abounding in the arctic Ocean, 
The Mysis relicta of Lovén is indeed quite certainly a depauperated descend- 
ent of that species, exhibiting, as it does, a very close resemblance to imma- 
ture specimens of the former’). A similar descent from true marine forms 
` may in all probability also be attributed to the other Mysidæ found to inhabit 
pure fresh water. 
The Mysidæ of the Caspian Sea are as far as is yet known all comprised 
within the subfamily Mysine, as defined by Mr. Czerniavsky, and belong to 
4 different genera, one of which is now for the first time established. Of the 
8 species enumerated in the following pages, 4 are as yet not known beyond 
the Caspian Sea, whereas the other 4 are stated to be common also to the 
Black Sea. As above stated, most of the Caspian species have already been 
described by Mr. Czerniavsky in his valuable work, «Monographia Mysi- 
darum imprimis Imperii Rossiciv. But, as these species are treated of in con- 
nexion with species from other parts of the Ocean, it is somewhat difficult 
at once to get a view of those occurring in the Caspian Sea. As moreover 
some of the species have been rather imperfectly described, and good habi- 
tus-figures are not at all given, I have thought it right to re-describe all the 
species, which I have had myself an opportunity of examining, and to give 
both habitus- and detail-figures of all. The descriptions are made as short 
and concise as possible, and are chiefly confined to the real distinctive cha- 
racteristics, the oral parts being, as a rule, only treated of in one species 
of every genus, as there are generally no appreciable differences to be found 
. Τα these parts in species belonging to one and the same genus. Good figures 
will on the whole make a minutely detailed description superfluous. To the 
descriptions are added short critical remarks on the validity of the species 
and its relation to other nearly allied species, as also information as to : 
occurrence and distribution. 
1) See G. 0; Sars, uem naturelle des Crustacées d'eau douce de Norvége I. p. 40. 
Mélanges biologiques. T. XIII, p. 
