32 • A REVISION OF THE BRITISH SPECIES OF 



But, so far as my observation extends, these characters are by 

 no means constant, individuals being frequently seen which 

 present in some points the characters of D. gracilis and in others 

 those of D. graciloides. One of the most remarkable characters 

 of D. gracilis in its typical form is the brush-bearing lateral 

 process of the outer branch of the left fifth foot in the male, but 

 specimens from Floutern Tarn, Lough Nascrahoge, and Wanstead 

 Park do not possess this appendage. Again, the males from 

 "Wanstead Park and Lough Neagh have the antepenultimate joint 

 of the right anterior antenna destitute of any lateral prolongation 

 (in this respect agreeing with D. graciloides), but those from 

 Lough ISTeagh do possess the lateral brush of the fifth foot, — 

 agreeing here with D. gracilis. The inner branch of the female 

 fifth foot in D. gracilis is one-jointed, but in specimens from 

 Talkin Tarn and other places we find it two-jointed. Lastly, 

 as regards the terminal claw of the male fifth foot : this organ, 

 in Talkin Tarn specimens and others, is S-shaped (a typical 

 graciloides character), while the external branch of the foot 

 possesses the characteristic setose brush of D. gracilis. Some 

 of the more interesting of these variations I here figure. The 

 character which seems to me most distinctive of D. gracilis, as 

 I understand it, is the angulated projection on the inner side of 

 the second joint of the protopodite of the left male fifth foot : 

 this prominence occurs in all specimens, so far as I know, 

 whether of gracilis or graciloides type, and I do not find that 

 it occurs in any other species, though a more extreme form of 

 a similar structure is figured by De Guerne and Eichard from 

 D. ffiseni, Lilljeborg. But, although not uniformly present, I 

 should set down as D. gracilis any specimen possessing the 

 minute setose papilla of the left male fifth foot or the short 

 hatchet-shaped process of the right male antenna. 



The localities from which I have notes of D. gracilis are as 

 follows : — Ponds at Wanstead Park and Wandsworth Com- 

 mon, Surrey (Mr. D. J. Scourfield) ; Chartners Lough and Crag 

 Lough, Northumberland, and most of the Lochs of the Scottish 

 Highlands (Rev. Dr. Norman) ; Loch Leven, Kinross (Mr. T. 

 Scott) ; Nostell Lake, Yorkshire ; Ellesmere Lake, Shropshire ; 



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