224 ON THE BEITISH SPECIES OE ENTOMOSTEACA 



which I look upon as belonging to the typical D. pulex, and the 

 principal abdominal processes are short, curved, nearly equal in 

 length, and divergent : the whole animal of a deep brown colour. 



Daphnia obtusa, Kurz., (PL IX., figs. 5-9). 



1874. Daphnia obtusa, Kurz., Dodekas neuer Cladoceren nebst 



einer Kurzen TJbersicht der Cladocerenfauna Bohmens, 



p. 16, pi. 1, figs. 8-9 (separate copy). 



Female. — Very like D. pulex, but smaller ; the posterior spine 

 almost obsolete, being rather a wide, acutely pointed angular 

 prominence than a distinct spine (fig. 5) : the lower margin of 

 the head is deeply excavated, the beak small but acutely pointed : 

 the prominence of the antennule very large and pouting : abdomen 

 and post-abdomen (fig. 6) as in D. pulex, except that the mar- 

 ginal spines are fewer, — only about eleven in number. Length, 

 1'8 mm. 



Male. — The valves of the male (fig. 7) are scarcely so much 

 tapered at the hinder extremity as in D. pulex, and the abdomen 

 (fig. 9) is destitute of the long dorsal process which normally 

 characterizes that species : the marginal spines of the post-abdo- 

 men are only about seven in number. Length, '85 mm. 



For specimens which I refer to this species I am indebted to 

 Mr. D. J. Scourfield, by whom they were taken in a pond at 

 Totland Bay, Isle of Wight. I have also found it in a shallow 

 pool on the line of the Roman wall near Garthside, Walton, 

 Cumberland (July, 1897), and in a pond at Burpham, Sussex. 

 Bishopton, county Durham (Eev. Canon Norman). 



Professor G. 0. Sars has kindly examined some of these speci- 

 mens and agrees with me in referring them to D. obtusa, Kurz, 

 at the same time expressing a doubt whether they are specifi- 

 cally distinct from D. pulex. The absence of any long dorsal 

 abdominal process in the male is doubtless a very striking char- 

 acter, though the amount of specific value attributable to it is 

 not by any means certainly ascertained, but if this point be 

 disregarded it will be extremely difficult to maintain a specific 

 distinction between the two species. , 



