272 A HISTORY OF EECENT CRUSTACEA 



The Greenland species, Mysis ocitlatus (0. Fabricius), is 

 of special interest on account of the variety relict a, Loven, 

 found in great hordes in several of the large freshwater 

 lakes of northern Europe, descended, it is supposed, from 

 ancestors which occupied those regions when the waters 

 were still salt and in connection with the open sea. In 

 Mysis relicta the antennal scale is elongate, ciliated all 



FIG. 22.Afysis relicta, Lovcn, 

 the first maxilla [Sars]. 



FIG. 23. J/JMI'S relicta, Loven, the second maxilla. 



round. Norman has obtained it from Lough JSTeagh in 

 Ireland, and by this discovery provides the genus Mysis 

 with at least one representative in the British fauna, after 

 despoiling it of all the rest. Sars, in his ' Histoire des 

 Crustacea d'eau douce de Norvege,' has given a most 

 elaborate description of this species, illustrated by highly 

 finished and most instructive plates, and more recently it 

 has been studied by Hansen with his accustomed acute- 

 ness. The accompanying figures in the text are copied 

 from Sars. Others from the same author are given in 

 Plate XIII. on a reduced scale. 



Macropsis, ' the long-eyed,' is the only other genus 

 agreeing with Mysis in the characters of the pleopods of 

 the male, and it is distinguished from Mysis both by the 

 extremely elongate ejes and by the structure of the first 

 antennas, which, in addition to the two flagella and the 

 setose appendage usual in the males of this family, have 

 the apex of the peduncle armed with yet a fourth process, 



