38 



combined, and only slightly divergent, dorsal keel well marked, inner edge 

 minutely ciliated; seta of outer edge not very far from the end, apical set! 

 not much elongated, the inner medial one about twice the length of the ramus 

 seta of inner corner more than twice as long as that of the outer. Anterior 

 antennae comparatively shorter and stouter than in the preceding species, reaching, 

 when refiexed, scarcely beyond the middle of the 2nd body-segment; number of 

 joints generally only 16, the 8th and 9th joints being confluent. Posterior an- 

 tennae with the terminal joint a little longer and narrower than the penultimate 

 one. Natatory legs with the rami moderately slender, terminal joint of outer 

 ramus in all pairs with only 2 spines outside; outer apical spine of inner ramus 

 in 4th pair very small and rudimentary. Last pair of legs resembling in shape 

 those in C> strenuus, the distal joint being rather short and stout, with the 

 lateral spine well developed and attached about in the middle. Ovisacs of moderate 

 size and oval in shape. Seminal receptacle comparatively small, resembling that 

 in C. alt/ssorum. 



Colour, according to Lilljeborg, somewhat variable, the body being in 

 some cases of a unitorm whitish grey hue, in other cases tinged with brownish 

 red or reddish yellow. 



Length of adult female about 1.70 mm. 



Remarks. This form was first described by the Russian naturalist 

 Uljanin, but was subsequently considered by Dr. Schmeil to be only a variety 

 of C. strenuus. Its specific distinctness has, however, been vindicated by Lillje- 

 borg, and I have myself, by an examination of specimens from Mongolia, had an 

 opportunity of confirming this view. The habitus-figure given in Dr. Schmeil's 

 work, as pointed out by Lilljeborg, evidently refers to this species, and also the 

 form described in Prof. Brady's Monograph as C. pulchellus, is unquestionably 

 referable to the same species. 



The most conspicuous character distinguishing this form from C. strenuus 

 is the very prominent lateral parts of the last 2 trunk-segments, in which 

 respect it somewhat resembles C. scutifer. It differs, however, very markedly 

 both from this and the 3 other species described above, in the armature of the 

 natatory legs, the terminal joint of the outer ramus having in all pairs only 2 

 spines outside. 



Occurrence. This form, it is true, has not yet been observed within the 

 limits of our country ; but I cannot doubt that, on a closer investigation, it will 

 be found to occur at any rate in the south-eastern part of the country, since 

 Lilljeborg has recorded it from immediately adjacent tracts of Sweden. The 

 figures here given are from specimens found in a sample taken in the delta of 



