water at ouce reveals a most peculiar and beautiful sculpture, 

 very conspicuous in specimens with winter-eggs (fig. 1). This 

 sculpture consists in numerous impressed pits arranged pretty 

 regularly in longitudinal rows and assuming on the dorsal part 

 af the carapace partly the character of a dense reticulation. 

 A somewhat similar sculpture is observed in another European 

 species of Alona, viz., A. guttata G. 0. Sars, as also in a species 

 of Chydorw, Ch. cad at us Schodeler. The inferior edges of the 

 valves are, as in most other species of this genus, fringed with 

 a dense row of delicate bristles, or cilia. 



The eye is not very large, and the crystalline lenses are 

 few in number and project but little from the pigment. 



The ocellus is much smaller than the eye, almost punctiform, 

 and located somewhat nearer to the eye than to the tip of the 

 rostrum. 



The antennulae are comparatively short and thick, almost 

 fusiform in shape, and exhibit, besides the terminal sensory fila- 

 ments, the usual delicate anteriorly pointing bristle; they do not 

 reach by far to the tip of the rostrum. 



The antennae are by no means powerfully developed, and in 

 structure agree with those in other species of the genus. The 

 branches are somewhat longer than the scape, both of them tri- 

 articulate and subequal in length, the lower with 4, the upper 

 with 3 natatory setae. Besides, each branch has at the tip a 

 strong spine, and a similar spine is affixed to the outer edge of 

 the upper branch. 



The lamellar projection of the labrum is rather large and 

 terminates posteriorly in an almost right-angled corner. 



The remaining oral parts and the legs do not exhibit any 

 marked difference in structure from those parts in other species 

 of the genus. 



The tail (fig. 2) is rather elongate and narrow, with the 

 supraanal angle projecting considerably. The outer part of the 

 tail, beyond this angle, is nearly parallel-sided, strongly com- 

 pressed, and somewhat obliquely truncated at the extremity. 

 Along the nearly straight dorsal edge a double series of den- 



