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as a rule, only in the deeper parts of the lakes, at depths varying from 3 to 

 12 fathoms, being never met with close to the border. As the species else- 

 where has also been observed in the sea, it constitutes most probably, as 

 suggested by Prof. Loven, a remnant of the ancient arctic fauna existing off' 

 the coasts of Europe and North America during the glacial epoch, a part of 

 which still remains in the more isolated marine basins, as the Baltic, whereas 

 another part, by the subsequent rising of the land, was left behind in some of 

 the lakes, where the present species, under certain circumstances, was enabled 

 to adapt itself to live in purely fresh water. 



Bistribtdion. — Several lakes of Sweden, Finland and Russia, as also 

 the great lakes of North America; the Baltic, Kattegat; the Kara Sea 

 (Hansen); coast of France (Chevreux). 



Gen. 2. Priscilla, Boeck, 1870. 



Body rather roljust, with powerfully developed metasome and urosome. 

 Tlie 4 anterior pairs of coxal plates very strong, curved downwards and 

 terminating each with an obtuse deflexed point tipped with long ciliated setae ; 

 5th pair very small. Antennae well developed, with the joints of the peduncle 

 densely setous; superior ones shorter than the inferior, and provided with a 

 rather large accessory appendage. Mandibles strong, of a similar .structure as 

 in Pontoporeia, })alp large and robust. First pair of maxillae with the termi- 

 nal joint of the palp scarcely expanded distally, basal lobe broadly triangular, 

 and edged with numerous ciliated setae. Second pair of maxillae with the 

 lobes nearly equal-sized. Maxillipeds about as in Fontoporeia. Gnathopoda 

 rather similar both in size and structure, propodos somewhat expanded, and 

 slightly subcheUform. Anterior pereiopoda of moderate size, dactylus quite 

 rudimentary; the 3 posterior pairs very powerful, and partly edged with 

 dense fascicles of spines, basal joint of the 3rd and 4th pair but little expan- 

 ded, that of last pair very large and laminar, edged with long ciliated setae. 

 Uropoda rather robust in structure, last pair with the rami very uno(iual. 

 Telson comparatively large, laminar, insinuated posteriorly. 



Remarlcs. — This genus established by Boeck exhibits, it is true, some 

 points of agreement with the preceding genus; but in several other characteristics 

 thus in the form of the coxal plates, the structure of the antennae and gnatho- 

 poda, as also in the powerful development of the 3 posterior pairs of pereio- 

 poda, it shows itself to be rather different, and somewhat reminds of the genus 

 HaHstoriiis. It contains, at present, but a single species. 



