On Fresh-water Eiitomostraca. 15 



ally by mounting the specimens in canada balsam, whereby 

 a sufficient transparency of the body could be obtained. 



5. Simocephalus gibbosus, G. O. Sars, n. sp. 

 (PI. 2, figs. 4—6). 



Specific Characters — Y Shell, seen laterally, ob- 

 liquely oval, widening posteriorly, and terminating with a 

 comparatively short and blunt median prominence; dorsal 

 margin for the greater part of its length, almost straight, 

 posteriorly, however, abruptly curved, forming a large and 

 very conspicuous, gibbous expansion just above the median 

 prominence, edges of the expansion closely denticulated. 

 Head of moderate size, less procumbent than in the prece- 

 ding species, front narrowly rounded, ventral edge scarcely 

 ascending, and slightly convex in the middle, rostral projec- 

 tion almost obsolete. Eye comparatively larger than in the 

 preceding species ; ocellus prolonged anteriorly into a narrow 

 stripe. Tail less broad, posterior edge above the anal sinus 

 scarcely expanded; anal denticles 10 — 12 on each side; 

 terminal claws quite smooth. Length of adult female 2 mm. 



Remarks. — This new species is allied to the European 

 8. vetulits, and has a similarly formed ocellus, but is at once 

 distinguished by the very conspicuous gibbous expansion of 

 the dorsal face posteriorly, which gives, the shell a peculiar 

 oblique shape. This expansion is even traceable in quite 

 young specimens. 



Description of the female. 



The length of fully adult, ovigerous specimens does not 

 exceed 2 mm., and this form, is accordingly rather inferior 

 in size to the preceding one. 



2 — Archiv for Math, og Naturv. B. XVIII No. 3. 



Trykt den 9de Juni 1896. 



