61 



35. Mesocyelops erassus (Fischer). 



(PI. XXXVII). 



pK craasus, Fischer, Beitrage zur Kenntniss der Cyclopiden (Fortsetzung). Bulletin Sue. Imp. 

 Nat. Moscou, Tome XXVI, Part 1, p. 92, PI. Ill, figs. 13 18. 



Syn: Cyclops oithonoides, var. hyalina, Schmeil. 

 liyalinus, Lancle, Richard, Lilljeborg (not Rehberg). 



Specific Characters. Female. Body rather short and stout, with the 

 iterior division oval in form, greatest width attaining fully half the length and 

 xrurring in the middle. Last trunk-segment small, though somewhat broader than 

 the 2 preceding species. Tail scarcely exceeding half the length of the 

 iterior division ; genital segment about the length of the 3 succeeding segments 

 )mbined, and somewhat tapered behind. Caudal rami unusually short and thick. 

 :arcely exceeding in length the anal segment, and somewhat divergent; seta of 

 iter edge very small and attached not far from the apex ; apical setae of mode- 

 rate length, the inner mediate one almost as long as the tail; seta of inner corner 

 more than 3 times as long as that of the outer, and not much shorter than the 

 outer mediate one. Anterior antennae somewhat less slender than in the 2 pre- 

 ceding species, reaching, when reflexed. about to the end of the 2nd segment, 

 lateral rib of the outer joints very slight. Posterior antennae nearly as in 

 M. oithonoides. Maxillipeds, however, comparatively smaller. Natatory legs 

 with the rami less slender and the apical spines shorter; those of inner ramus 

 in 4th pair less unequal, the inner one being scarcely more than twice as long as 

 the outer and much shorter than the terminal joint of the ramus; connecting 

 lamella of this pair with the projections of the hind edge coarsely dentate. 

 Last pair of legs resembling in shape those in M. oithonoides, though having 

 the distal joint somewhat smaller and the apical setae comparatively shorter. 

 Ovisacs rounded oval in form and generally containing only a limited number 

 of ova. Seminal receptacle about as in M. oithonoides. 

 Body very pellucid, with a faint yellowish tinge. 

 Length of adult female about 0.80 mm. 



Remark*. The identity of the above-described form with Fischer's 

 ('//clops erassus seems to me evident. It has erroneously been identified by 

 Dr. Schmeil and several other authors with C. hyalinus Rehberg, which, as 

 stated above, is unquestionably a typical M. oithonoides. From the latter species 

 it is at once distinguished by its much shorter and stouter body, and by the unu- 

 sually short and thick caudal rami, thus fully deserving the specific name pro- 

 posed for it by Fischer. In these respects it much more resembles the African 

 species, M. neglect/UB G. 0. Sars, which however differs in the much shorter 

 innermost caudal seta. 



