33 



Colour generally light yellow or orange. 



Length of adult female 1.50 1.70 mm. 



Remarks. The present species is in all probability identical with the 

 form named by Jurine Monoculus quadricornis rubens, and also Cyclops pictus 

 of Koch may be the same species. As, however, some doubt might arise about 

 the identity, this species has generally been recorded under the name proposed 

 by Fischer, who indeed was the first to give a recognisable description of it. 

 Both C. brevicaudatus, Claus and C. Clausi, Lubbock are undoubtedly referable 

 to the present species, which may be regarded as the type of the genus Cyclops 

 as defined here. 



Occurrence. This is one of our commonest Cyclopses, being very abundant 

 in small ponds and tarns, especially early in the spring. It is not. like most 

 other species of the present genus, a strict bottom-form, but is generally found 

 close to the surface of the water, swimming about rather quickly in the usual 

 jumping manner. Male specimens are at first rather scarce, but become more 

 numerous later in the season. Two varieties occur, the one of rather smaller 

 size than the other and of lighter colour, and found in somewhat larger tarns. 

 I have, however, failed to detect any other difference between the 2 forms. 



Distribution, Throughout Europe, central and northern parts of Asia, 

 Bear Island, Spitsbergen, Algeria. 



15. Cyclops abyssorum, G. 0. Sars. 



(PI. XVII). 



Cyclops abyssorum, G. 0. Sars, Oversigt af tie indenlandske Ferskvandscopepoder. Chr. Vid. 



Selsk. Forhandl. 182, p. 29. 



Syn. : C. strenuus, var. temdpes, G-. 0. Sars. 



Specific Characters. Female. Body comparatively more robust than in 

 C. strenuus, with the anterior division more tumefied in its anterior part. Cephalic 

 segment obtusely rounded in front. Lateral parts of penultimate trunk- segment 

 terminating in a well-marked dentiform point curving outwards. Last trunk- 

 segment acutely produced laterally. Genital segment considerably dilated in front, 

 its greatest width exceeding the length. Caudal rami very slender and narrow, 

 exceeding somewhat in length the last 3 caudal segments combined, and rather 

 divergent, each having dorsally a very distinct longitudinal keel, inner edge coarsely 

 ciliated, seta of outer edge small and attached near the end, apical setse com- 

 paratively longer and thinner than in C. strenuus, the inner medial one almost 

 attaining the length of the tail, seta of inner corner twice as long as that of the 

 outer. Anterior antennae much more slender and elongated than in C. strenuu*, 



5 Crustacea. 



