1910.] 



BRITISH SPECIES OF OSTRACODA. 



195 



be grouped under two families or subfamilies, Candonince, and 

 Jlerpetocypridince, broadly separable from each other by the dis- 

 tinctly bisexual character of the former, with accompanying 

 sexual reproduction, and the non-sexual (or hermaphrodite) 

 character of the latter with a constant " parthenogenetic " repro- 

 duction. It is to be remembered, however, that in some cases 

 which at one time were believed to constitute examples of 

 " parthenogenetic " reproduction, males have been found to exist ; 

 and it is possible that the existence of that sex may hereafter be 

 demonstrated in the case of other species. The number of species 

 hitherto recognized as natives of the British Islands is only twenty- 

 nine. This number will doubtless be considerably increased when 

 various areas, at present but little known, have been thoroughly 

 examined. The only parts of the country which can be said to 

 have received anything like a complete investigation are : — (1) the 

 southern counties of Scotland, which have been most diligently 

 overhauled by Dr. Thomas Scott of the " Fishery Board for 

 Scotland " and the late Dr. David Robertson of Cumbrae ; (2) the 

 counties of Northumberland and Durham and — less completely — 

 Cumberland and Westmorland, where the Rev. Dr. Norman 

 and myself have worked for many years ; (3) the Fen District of 

 East Anglia including the Norfolk Broads and the Cambridgeshire 

 Fens, which have been fairly well investigated by Dr. Robertson 

 and myself, and more recently by Mr. Robert Gurney and others. 

 But even in these well- worked districts, much, no doubt, remains 

 to reward future investigators.* The species here recorded are 

 as follows : — 



Candonince. 



Candona Candida O. F. Miiller, 



„ angulata G. W. Miiller. 



„ neglecta G. O. Sars. 



„ caudata Kaufmann. 



,, siliquosa G. S. Brady. 



„ elongata Brady <$• Norman. 



„ pvotzi BZartivig. 



,, zenekeri G. O. Sars: 



„ stagnalfs G. O. Sars. 



„ calecfonise G. ff. Brady. 



,, lactea Baird 1 . 



Candona fragilis Bartwig. 



„ fabseformis Fischer. 



s , hyalina Brady $ Robertson. 



„ brevis G. W. Midler. 



„ pubescens Koch. 



„ rastrata Brady Sf Norman* 



,i euplectella Robertson. 

 Candonopsis kingsleii Br. <${ Robertson.- 



„ scourfieldi G. S. Brady. 



Siphlocandoua similis Baird. 



„ iiofiaaiii G. S. Brady. 



Heryetocypridince. 



Herpetocypris reptans Baird. 



„ chevi'euxii G. O. Sars.- 



„ sti-igata O. F. Miiller. 



Prionocypris serrata Normaw. 



Prionoc3'pris tttinefa'cta Br. 8f Robertson. 

 llyodromus robertsoni Br. & Norm. 

 ,-, oiivacisus Br. 8f Norm. 



* The differences between so-called species are in many cases so small, and withal 

 so inconstant, that the diagnosis becomes a matter of considerable difficulty. I have 

 therefore attempted in this paper to place such species- on a rather more stable 

 footing — being at the same time quite aware Shat the attempt is only partially 

 swceessful. 



1,°,* 



