70 



Gen. 15. LeptOCydOpS, (i. O. Sars, n. 



Generic Character*. Body more or less slender, with the 2 chief divisions 

 very sharply defined. Epiraeral parts of the trunk-segments, as a rule, distinctly 

 prominent laterally, especially those of penultimate segment, though rounded at 

 the extremities. Last trunk-segment short and broad, being produced on each 

 side to a narrowly rounded and densely hairy lobe, somewhat impinging upon 

 the base of the genital segment. Tail very slender and narrow, with the genital 

 segment comparatively short and abruptly contracted immediately behind the 

 base. Caudal rami more or less prolonged, and in most cases exhibiting along 

 the outer edge a delicate denticulation ; seta of this edge small and not far from 

 the end; middle apical seta? slender and elongated, being, as a rule, clothed on 

 the proximal part with scattered coarse hairs; seta of inner corner of incon- 

 siderable length and very thin, that of the outer corner more or less spiniform. 

 Anterior antennae in all the known species composed of 12 joints, the outer ones 

 generally very slender and narrow. Posterior antennae and oral parts on the 

 whole of normal structure. Natatory legs well developed, with 3-articulate rami; 

 1st pair, as usual, the smallest, and having the 2nd basal joint conically pro- 

 duced at the inner corner and provided with a long deflexed spine ; armature of 

 the rami as in the genus Pachy Cyclops. Last pair of legs very small, each 

 forming a simple somewhat trilobate lamella armed inside with a denticulated 

 spine, outside and at the conically exserted tip with a slender seta. Ovisacs 

 generally oval fusiform in shape. Seminal receptacle with the posterior part 

 not produced, forming 2 transverse bands defined in the middle by a slight 

 emargination. 



Remarks. The type of this genus is the species generally described 

 under the name of Cyclops serrttlutus Fischer, with which Dr. Schmeil has con- 

 nected another rather diviating form, C. /trn.^nui^ Fischer, to form a particular 

 group of Cyclopses, viz.. his "serrulatus-prasinus group". The most prominent 

 character distinguishing this genus from the 3 preceding ones, is undoubtedly the 

 very different structure of the last pair of legs. Several other characters common 

 to the greater number of the species comprised within this genus may also be 

 adduced, and are shortly enumerated in the above diagnosis. The genus seems 

 to be very rich in species; but most of these are so closely related to each 

 other, that they can be distinguished only by a careful examination, and for 

 this reason they have been regarded by most earlier authors as only varieties 

 of one and the same species, viz., C. serrulatus of Fischer. In the following 



