On Fresh-water Entomostraca. 



Description of the female. 



a. Typical form. 

 (PL 1, figs. 1, 2). 



This form, or variety, agrees closely with that described 

 and figured by Mr. King as the «common form», and is 

 probably derived from the very same locality as the latter. 



The length of the largest specimens examined measures, 

 without the spine, 4,70 mm.; but the greater number of the 

 specimens are considerably smaller, though ovigerous. 



The form of the shell, when seen laterally (fig. 1), is 

 oblong oval, and considerably narrowed posteriorly towards 

 the base of the spine, with the dorsal margin evenly convex 

 in the middle, and forming anteriorly, in the cervical region, 

 a very slight concavity. The spine, which issues from 

 near the middle of the posterior extremity, is rather eloug- 

 ated, exceeding half the length of the shell, and is perfectly 

 straight, but somewhat upturned. 



The head appears considerably narrower than the shell, 

 and somewhat irregularly rounded in front, with a slight 

 indication of an angle in the ocular region. Its ventral 

 edge is somewhat oblique, and forms a perfectly straight 

 line as far as the tip of the rostrum, which is accordingly 

 not deflexed, though terminating in a very acute point. 

 The dorsal crest, the limits of which are shown by the 

 insertion of the muscles moving the antennæ, is not very 

 largely developed, though distinct all round the head. The 

 fornix appears, in the lateral view of the animal, as a curved 

 elevated line extending from the ocular region to the point 

 where the valves take their origin, and in this place pro- 

 jecting as a spiniform corner. The posterior half of the free 

 edges of the valves is closely denticulated, the denticles 



