claws slender and distinctly denticulated, natatory setae extending to the tips 

 of the claws. Spines on the outermost masticatory lobe of the maxillae smooth. 

 Palp of maxillipeds of moderate size, with the apical setae unusually prolonged, 

 the middle one exceeding the palp in length and distinctly ciliated in its 

 outer part. Anterior legs moderately slender, with the terminal part distinctly 

 4-articulate and the apical claw rather elongated. Posterior legs with the apical 

 chela well developed. Caudal rami almost straight and gradually attenuated, 

 apical claws only slightly curved and rather unequal in size, the distal one 

 considerably exceeding half the length of the ramus. 



Colour dull grassy green. 



Length of adult female amounting to 2.30 mm. 



Male unknown. 



Remarks. The present species, the identity of which with Monoculus 

 virens of Jurine seems to me to be indoubitable, may be regarded as the type 

 of the genus Eucypris. It is easily distinguished from the other 2 species 

 here described by its much larger size, as also by the rather different shape 

 of the shell. In these respects it comes however very near to some of the 

 exotic species described. G. W. Miiller distinguishes of the present species 3 

 varieties or subspecies named media, obtusa and acumiimta. Of these the 

 1st agrees pretty well with the Norwegian specimens observed by me; the other 

 2 I am much inclined to regard as particular species, having had an oppor- 

 tunity of examining both of them from specimens raised out of dried mud 

 from Algeria. Young specimens of the present species, as usual, differ some- 

 what from the adults in the shape of the shell, and are moreover highh 

 distinguished by a most peculiar and beautiful sculpture of the valves exactly 

 agreeing with that described and figured by Brady in his Cypris tessellatc 

 (see the figures on the accompanying plate). 



Occurrence. This is one of our commonest freshwater Ostracoda, being 

 found often in great abundance in grassy ponds and swamps, especially in the 

 early part of the summer. In. habits the animal is rather active and is often 

 seen to swim about in the water with considerable speead, though as usual, 

 more generally keeping at the bottom for search of food. Male specimens 

 have never been met with either of this or any other species referable to the 

 present genus in the restriction here adopted, and the exclusive partensgenitica 

 propagation may thus be mentioned as a distinguishing character of the genu 

 from some of the succeeding nearly allied genera. 



Distribution. Throughout Europe, North America, Greenland. 



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