ii2 The Irish Naturalist. May, 



NOTES ON IRISH CLADOCERA. 



BY W. F. DK V. KANE, M.A. 



The publication of that most valuable work " Cladocera 

 Suecica" by Wilhelm Lilljeborg will give a great stimulus to 

 the study of this group of the Entomostraca, illustrated as it 

 is by 87 plates of large and beautifully- executed figures. No 

 less than 21 plates are devoted to the most perplexing genus 

 Bosmina. A cursory examination of the text and plates 

 induces me to send a short memorandum relating to certain 

 Irish species, which during the past two years, I have met with. 

 Prof. Lilljeborg has sunk the specific name of Bosmina 

 Lilljeborgii G.O.S., and made it a varietal name of B. mixta 

 (nov. nom.) of which he describes another variety humilis; 

 and byre-examination of a number of the specimens collected 

 in Lough Erne it would seem that the Irish form offers some 

 characters of specialization, and on the whole approaches 

 more nearly to the new variety humilis than to that named by 

 Sars after Lilljeborg. The distinctive characteristics of the 

 latter are set down as having the shell as high as it is broad ; 

 a concavity in the contour behind and above the head ; and 

 the rostra as long or scarcely shorter than the length of the 

 shell. The Lough Erne Bosmina rarely shows the concavity, 

 and is frequently of greater breadth than height, and the rostra 

 usually are not of the prescribed length. On the other hand 

 it differs from both varieties, especially humilis, in having the 

 postero-ventral shell-spines almost absent, thus approaching 

 the species B. coregoni Baird. 



Another Lough Erne cladoceran, Bythotrephes Lilljeborgii 

 (now B. Cedcrstroemii Schoedler), is most exhaustively 

 illustrated, and there can be no doubt of the identity of our 

 species. Similarly, Lilljeborg throws further light upon the 

 two species of Diaphanosoma, hitherto named with some 

 hesitation ; and it would appear that both have been correctly 

 recorded from Ireland, D. brandtianum now being referred 

 to D. leuchtcribergianum Fisch. A notable feature of fche book 

 is the careful distinction made between the varying forms of 

 the Bosminidcz and other genera at different seasons of the 

 year. If these seasonal variations prove to be relatively 



