72 D. J. SCOURFIELD ON AN ALONA AND A PLEUROXUS NEW TO BRITAIN. 



meriting in a modest way the Cladocera Sueciae, and making 

 it available as a complete monograph of the known British 

 species. 



Alona weltneri Keilhack. 



As long ago as 1895 my friend Dr. T. Scott sent me, from a 

 collection made in a little pool on the Castle Hill at Scarborough, 

 a specimen of an Alona which did not agree with any of the 

 species then known to us. As, however, it was closely allied 

 to A. costata, and only one specimen had been found, it was 

 not described as a new species, and has, in fact, remained un- 

 recorded until the present time. Upon receiving a copy of L. 

 Keilhack's paper, " Zur Cladocerenfauna des Madiisees in 

 Pommern " (Archiv fur Natitrgeschichte, 71. Jahrgang, 1. Bd., 

 1905, pp. 138 — 162), I at once saw that the form therein 

 described as A . weltneri (p. 158) was, without much doubt, the 

 same as the dubious Alona from Scarborough, a view which is 

 also shared by Herr Keilhack himself, who has very kindly 

 compared tracings of my drawing with his original specimen. 



The general appearance of this species is shown in Fig. 1, 

 which is a reproduction of the drawing of the Scarborough 

 specimen made in 1895. (Unfortunately, this specimen has been 

 lost, so that it is impossible to give any further details than those 

 mentioned in this paper.) It will be seen that, as already stated, 

 this species is very nearly related to A. costata in all respects 

 except the post-abdomen. The outline of the shell is somewhat 

 quadrangular, but the dorsal line is well arched, and runs 

 into the posterior margin without producing a noticeable angle. 

 The shell-markings consist of longitudinal lines placed at a 

 moderate distance apart. The eye-spot is smaller than the eye, 

 and nearer to the latter than to the tip of the rostrum. The 

 antennules reach almost to the end of the rostrum. The 

 appendage on the labrum is large and well rounded, but slightly 

 truncated posteriorly (Fig. 4). The second antennae (Fig. 3) 



