NORMAN ON THE GENUS MYSIS 271 



more than half the length of the fourth.' Mysis Helleri, 

 Sars, a Mediterranean species also found at the Channel 

 Islands and on the coast of Devon, is very like in general 

 character to Mysis spiritus, from which, Norman observes, 

 it may be at once distinguished by the very short and 

 nodulously swollen first articulation of the subdivided sixth 

 joint in the trunk-legs. Mysis Lamornce, Couch, has the 

 telson deeply but narrowly cleft. Mysis arenosa, Sars, is 

 a, small species in which the pleon is shorter than usual, 

 the eyes are short, the fourth pleopods of the male do not 

 reach the apex of the telson, the incision in the telson is 

 about one-fourth of its length. This species, first described 

 from the Mediterranean, has since been found in South 

 Devon and in Scotland. Thus nine species of the genus 

 have been assigned to the British Fauna. In the ' Annals 

 and Magazine of Natural History ' for September, 1892, 

 Canon Norman has distributed these species among four 

 genera, in which the distinctions depend chiefly upon the 

 remarkable and varied modifications of the pleopods in the 

 male sex. and upon the form of the antennal scale. Under 

 this arrangement the species jiexuosus, neglecta, and inermis, 

 are referred to Macromysis ; spiritus, ornata (including Ker- 

 villei), arenosa, Helleri, and Parkeri, to Schistomi/sis ; and 

 vulgaris to Neomysis. Mysis Lamornce is transferred to 

 Hemimysis. As already observed, for Macromysis must be 

 substituted the older name Praunus. The species Parkeri, 

 Norman, 1892, from South Devon, is a new one. It is 

 very near to Schistomysis spiritus, from which it may be 

 distinguished by the more twisted and bent inner uropod, 

 armed with about fifteen spines on the inner margin, 

 increasing in size from the base of the appendage. In 

 Schistomysis the antennal scale is sub-rhomboidal, with 

 the apex greatly produced beyond the spine of the unciliated 

 external margin ; in Neomysis this scale is ciliated on both 

 margins, and runs out to a spine-like apex. The species 

 Themisto longispinosa, Goodsir, and Themisto lyrevispinosa, 

 Goodsir, from the Firth of Forth, are evidently male forms 

 of the genus Mysis, but their specific identity has not been 

 determined. The generic name Themisto is preoccupied. 



