63 



Fischer, which, as stated above, is the form described by him as C. Inyalinus. 

 Though nearly allied to that species, it may easily be distinguished by the somewhat 

 different shape of the caudal rami, and more particularly by the comparatively 

 short innermost apical seta. In the living state it is moreover at once recognised 

 by the peculiar colour of the body. 



Occurrence. I have met with this form only quite occasionally in some 

 small lagunes at the border of the lake 0stensj0 near Christiania, and also in 

 wide expanses of the river Glommen, at Nipen. 



Distribution. Sweden (Lilljeborg), Germany (Schmeil), Poland (Lande). 



37. Mesocy clops gracilis (Lilljeborg). 



(PL XXXIX). 



Cyclops gracilis, Lilljeborg, De crustaceis ex ordinibus tribus in Scania occurrentibus, Appendix, 



p. 208. 



Specific Characters. Female. Body very slender, resembling in outward 

 appearance that of M. oithonoides, the anterior division being narrow oblong in 

 outline and contracted behind, with the greatest width quite in front. Last trunk- 

 segment very small, with the lateral parts rounded off. Tail slender, equalling 

 in length about 2 / 3 of the anterior division; genital segment attaining the length 

 of the 3 remaining segments combined, and slightly tapered behind. Caudal 

 rami somewhat longer than the anal segment and slightly divergent; seta of outer 

 edge attached in the middle; apical setae comparatively short, the inner mediate 

 one scarcely exceeding half the length of the tail; seta of inner corner only 

 slightly longer than that of the outer, and scarcely half as long as the outer 

 mediate one; dorsal bristle of moderate length. Anterior antennae long and 

 slender, reaching, when reflexed, to about the middle of the 3rd segment, and 

 composed of only 11 joints clothed with very long, diverging, partly ciliated 

 setse. Posterior antennae likewise comparatively slender, with the terminal joint 

 longer than the penultimate one, lateral bristles of the latter joint reduced in 

 number. Maxillipeds rather fully developed resembling in structure those in the 

 other species of the present genus. Natatory legs, on the other hand, imper- 

 fectly developed, the rami in all of them being composed of only 2 joints; 1st 

 joint of outer ramus in 4th pair without any seta inside; apical spines of inner 

 ramus in same pair very unequal, the outer one being quite rudimentary, the 

 inner long and slender. Last pair of legs likewise imperfectly developed, the 

 proximal joint being quite confluent with the segment, distal joint extremely small, 

 rod-like, and carrying on the tip 2 very unequal setse, the inner one being quite 

 rudimentary. Ovisacs comparatively small arid rounded oval in shape, each con- 



