129 



region, ventral margin gently sinuated, anterior extremity somewhat deflexed 

 and obliquely rounded, posterior blunted, with the lower corner rounded off; 

 seen dorsally, narrow oblong, with the greatest widht behind the middle 

 and about equal to ~h, of the length, anterior extremity gradually narrowed to 

 an acute point, posterior extremity more obtuse. Valves conspicuously unequal, 

 the left one considerably overlapping the right in front as also along the 

 ventral face, exhibiting moreover a well defined marginal zone closely striated 

 transversally; inner duplicatures rather broad in front and of somewhat diffe- 

 rent shape in the 2 valves; surface of shell smooth and clothed anteriorly with 

 delicate densely crowded hairs, posteriorly with scattered rather long bristles. 

 Natatory setae of posterior antennae much reduced, scarcely extending to the 

 middle. of the succeeding joint. Caudal rami rather slender and slightly curved, 

 with the base somewhat thickened, dorsal edge fringed with 4 5 successive 

 rows of very minute spinules, distal claw not attaining half the length of the 

 ramus, but nearly twice as long as the proximal one, both distinctly denti- 

 culated, dorsal bristle very small, apical one very much longer. 



Colour more or less olivaceous green, clouded with darker shadows. 



Length of adult female amounting to 2.60 mm. 



Male unknown. 



Remarks. This form vas described as early as the year 1850 by Baird, 

 but was erroneously referred by that author to the genus Candona. It is one 

 of our largest fresh water Ostracoda, and easily recognisable from any of them 

 by its elongate reniform shell, resembling however in this respect closely some 

 of the foreign species, for instance the African species, H. Chevreuxi G. O. 

 Sars, yet exhibiting some well marked differences, in particular as to the relative 

 developpement of the natatory setae on the posterior antennae. 



Occurrence. I have met with this Ostracod occasionally both in the 

 neighbourhood of Christiania and near Trondhjem. It is generally found in 

 teams and ditches with muddy bottom, and always close to the ground, along 

 which it is seen crawling rather slowly, at times burrying more or less deeply 

 within the loose mud. I have never seen it to make even the slightest attempt 

 to move freely in the water. 



Distribution. Throughout Europe. 



16 Crustacea. 



