154 



segments considerably expanded, terminal part scarcely longer than the dista 

 segment, and having the 3 articles of about equal length. Posterior antennae with 

 the apical claws slender and successively diminishing in length behind. Vibrator} 

 plate of mandibular palp oblong quadrangular in shape and edged with 5 setae 

 3 apical and 2 much smaller lateral. Legs with the basal seta very coarse 

 and densely hairy, apical claw almost straight. Genital lobes terminating below 

 in a rounded lappet. 



Colour of shell dark brownish, limbs bright yellow. 

 Length of adult female amounting to 0.95 mm. 



Remarks. This form was described as early as the year 1863 by the 

 present author as a species of Cythere, and was subsequently referred by Brady 

 to the genus Cytheridea Bosquet. It has generally been regarded as nearly 

 allied to Cyprideis lorosa Jones, and indeed G. W. Mtiller records it only as a 

 variety of that species. This is certainly quite erroneous. The present form 

 is in reality so considerably different, that in my opinion it cannot even be 

 placed in the same genus with it. 



Occurrence. I have taken this form rather abundantly in severals of our 

 larger lakes, for instance in Mjosen, Tyrifjord, Aarungen, Noklevand etc., and 

 have also met with it in one of our montain lakes, viz., in Afsio, on the high- 

 plateau of Dovre. It occurs generally in a depth of some fathoms, on a muddy 

 bottom, along which the animals crawl slowly in the usual manner of the 

 Cytheridae. Though I have examined carefully many hunderds of specimens 

 from different localities, I have never come across any male, and the same 

 absolute want of this sex has also been ascertained by other authors. It would 

 thus seem to be sufficiently proved, that the reproduction of the present form, 

 unlike what is generally the case with Cylheridae, is exclusively parthenogenetical. 

 Distribution. Sweden, British Isles, Switzerland. 

 Fossil. Scotland. 



Gen. 32. Cyprideis, Jones, 1856. 



Syn: Cytheridea, auctomm (part). 



Generic Characters. Shell of somewhat various shape, rather solid, and 

 distinctly sculptured, in some cases provided with lateral protuberances. Valves 

 somewhat unequal, the right one armed at the infero-posteal corner with a denti- 

 form process, marginal zone densely striated. Hinge exhibiting a more or 

 less distinct crenulation of the edges. Eyes distinctly separated. Anterior 

 antennae about as in Cytherissa; posterior comparatively less robust, and on 



