88 



Colour of female generally bluish, of male reddish orange. 



Length of adult female 2.00 mm., of male 1.50 mm. 



Remarks. This form was at first (in the year 1863) erroneously described 

 by the present author as D. castor (Jurine). The same form was subsequently 

 examined by Mr. Wierzejski, who at first regarded it as only a variety of 

 D. gracilis, G. 0. Sars, but in a subsequent paper recorded it as a distinct 

 species under the above name. Prof. Lilljeborg assigned to this form the provi- 

 sional name D. hamatus, on account of the hook-like projection of the last joint 

 of the right anterior antenna? in the male, and the name proposed by Mr. Wier- 

 zejski also refers to the same character. In addition to this character, the present 

 species may be easily recognized by the form of the lateral expansions of the 

 last pedigerous segment in the female, and also by that of the genital segment. 

 The last pair of legs, moreover, exhibit in both sexes several well-marked pecu- 

 liarities. 



Occurrence. I have found this form very abundantly in the neighbourhood 

 of Christiania, especially in small ponds, but sometimes also in larger lakes. 

 It also occurs in many other places in Norway, both in the lowland and in the 

 mountain districts, and extends northwards as far as Bodo. 



Distribution. Sweden (Lilljeborg), Tatras Mountains (Wierzejski), Switzer- 

 land, France (Richard), territory of Akmolinsk, Central Asia (Lepeschkin). 



36. Diaptomus bacillifer, Koelbel. 



(PI. LX). 

 Diaptomus bacittifer, Koelbel, Cavcinologisclies. Sitzuugsber. d. K. K. Akad. Wiss. Wien. Vol. XC\ 



Syii: Diaptomus montanus, Wierzejski. 



i-ifs, Lilljeborg, M. S. 



Specific Characters. Female. Body somewhat robust, with the anterior 

 division, seen dorsally, oblong oval in form, greatest width considerably exceeding 

 Vs of the length, and occurring somewhat in front of the middle. Lateral expansions 

 of last pedigerous segment somewhat resembling those in D. denticornis, but less 

 distinctly biangular. Genital segment fully twice as long as the other 2 caudal 

 segments combined, and slightly dilated in front, with a very small denticle on each 

 side. Caudal rami about twice as long as they are broad. Anterior antennoe, 

 when reflexed, reaching about to the middle of the genital segment. Last pair 

 of legs with the inner ramus much shorter than the 1st joint of the outer, but 

 distinctly biarticulate, tip blunted and somewhat incurved, with a very small hair 



