D. J. SCOURFIELD ON AN ALOXA AND A PLEUROXUS NEW TO BRITAIN. 75 



very close to one another, they often seem to form one continuous 

 row of nearly double the number occurring on one side alone. 

 This can be seen from Figs. 9 and 10. The teeth as they 

 approach the anus are accompanied by an increasing number of 

 fine setae, and the two anterior ones appear to consist chiefly of 

 such setae, the tooth properly so called being simply the longest 

 and stoutest of the series. On each side of the post-abdomen, 

 just above the teeth, is a line of exceedingly minute setae, 

 arranged, as is usually the case, in a series of curved 

 groups. 



Compared with the Devonshire specimen, the American 

 examples exhibit in nearly all cases a distinctly longer rostrum, 

 the tip being rather over than under twice as far from the 

 eye-spot as the latter from the eye. The outline of the shell 

 varies considerably, and in some cases the markings are practically 

 non-existent. There is a marked tendency, although it does not 

 amount to a constant feature, for the posterior dorsal angle of 

 the post-abdomen to be drawn out into an irregular little 

 projection, on which are situated the first two or three teeth. 

 Figures of two American varieties of the species have been given 

 by C. L. Herrick in his Final Report on the Crustacea of 

 Minnesota (1884), and again in Herrick and Turner's Synopsis 

 of the Entomostraca of Minnesota (1895). I have not been able 

 to refer to the original description by Birge. 



The length of the Devonshire specimen is ■£$ in., and the 

 average size of the American specimens is about the same. 



Explanation of Plate 8. 



Fig. 1. Alona weltneri Keilhack, $ , x 95. 



» 2. ,, n post-abdomen, x 350. 



» 3. „ „ second antenna, x 350. 



j) 4. ,, „ process on labrum, x 200. 



