31 
inside, and a row of ciliated setse outside, its distal joint scarcely half as long 
as the proximal one, and carrying on the tip a remarkably strong spine accom¬ 
panied by a long seta; outer ramus densely clothed with ciliated setse. Body 
without any pigmentary ornament, of whitish colour, changing in female to pale 
yellow. Length of adult female reaching to 12 mm., of male to 10 mm. 
Remarks .—This form was first described by Kroyer as a species of 
Cuma, but was subsequently separated as the type of his genus Leucon. It is 
the largest of the Norwegian species, and moreover easily recognizable by its 
very slender form and the nose-like, upturned pseudorostral projection. In the 
young, not yet sexually mature state, the male does not exhibit any pronounced 
difference in its general appearance from the female, the form and armature of 
the carapace being the very same in both. It is quite otherwise when the male 
has reached full sexual maturity. In this state, on account of the peculiar 
transformation of the carapace, it looks so very different from the female that 
even in quite recent times, its true relation has been wholly misapprehended. In¬ 
deed, there cannot be any doubt that the form recently recorded by Mr. Walker 
as Leuconopsis ensifer is nothing else than the adult male of the present species. 
As will be shown farther on, an altogether analogous transformation of the male 
is proved to take place in all our other species of this genus. 
Occurrence .—This is one of the commonest Cumacea of the Norwegian 
coast, occurring very frequently throughout its whole length, from the Christiania 
Fjord to Yadso, in depths from 30 to 100 fathoms, soft muddy bottom. The 
adult males seem, only at certain seasons, to appear in some numbers. They are 
extremely agile, swimming about with great rapidity by the aid of the very fully 
developed exopodites, and the likewise well-developed 2 pairs of pleopoda. The 
females, on the other hand, lead a much more stationary life, mostly dwelling on 
the bottom, in which they are able to bury themselves with great dexterity. 
Distribution .—British Isles (Norman), Kattegat (Meinert), Heligoland 
(Ebrenbaum), Greenland (Hansen), the Kara Sea (Hansen), Atlantic coast of 
North America (Verrill). 
2. Leueon nasieoides, Lilljeborg. 
(pi. xxm.) 
Leucon nasicoicles, Lilljeborg, Ofvevs. af Vet. Akad. Fork. 1855, p. 122. 
Specific Characters . — Body of female considerably shorter and more robust 
than in the type species, with the tail scarcely exceeding in length the anterior 
division. Carapace rather deep, and about the length of the exposed part of 
