146 



ventral margin very slightly sinuated and curving evenly upwards behind, 

 anterior extremity narrowly rounded, posterior much broader and somewhat 

 obliquely blunted, more prominent above; seen dorsally, elongate ovale or 

 lanceolate in outline, with the greatest width behind, and about equalling the 

 height, anterior extremity gradually narrowed to an obtuse point, posterior ob- 

 tusely rounded off. Valves slightly unequal, the right somewhat encompassing 

 the left in the posterior part; surface smooth and polished, with a pearly lustre, 

 and almost bare from hairs; muscular spots 9 in number, somewhat wedge-shaped 

 and arranged regularly around a common centre. Eye well marked and oc- 

 curring far in front. 



Colour of the shell whitish pellucid, with a dark patch just above the 

 muscular spots. 



Length of adult female 0.72 mm. 



Remarks. This remarkable form is eastily recognised from any of our 

 other freshwater Ostracoda by the narrow cuneiform shape of the shell, and 

 still more by the anomalous structure of the several appendages. The form 

 recorded by Turner from North America, under the name of D. improvisa, is 

 certainly identical with the present species. 



Occurrence. The only place, where I have met with this Ostracod is in 

 the lower part of the .Vansj0 near Moss. It occured here occasionally on a 

 muddy bottom, at a depth of about 2 fathoms. The specimens were not easy 

 to detect, as they were mostly hidden within the mud, through which they 

 move very slowly, chiefly by the aide of their powerful antennas. All the 

 specimens captured were of the female sex, and were mostly loaden wit ova 

 and embryos in their shell-cavity. Brady has also observed the male, and has 

 given a figure of the copulative appendages, no other structural details being 

 however noted. 



Distribution. Sweden, British Isles, France, Switzerland, North America. 



Fam. 2. Cytheridae. 



Characters of the family. Shell much varying in shape and structure, 

 but more generally of rather firm consistency, more or less calcareous, and 

 not seldom roughly sculptured. Valves, as a rule, not much unequal, and 

 connected dorsally by a more or less perfect hinge; muscular spots arranged 

 in a vertical row. 2 eyes generally present, in some cases however conflue 



