212 The Irish Nahiralist. August, 



D. kahlb€ig€7isis and what was hitherto termed D. lacustris, 

 var. galcata, since this mark seems often present in very 

 minute form in D. kahlbe7'gc7isis ; while from other specimens 

 which could not be examined alive, this criterion seems 

 absent, having disappeared, owing to their being slightly 

 deteriorated in condition. The helmeted forms are now 

 classed by Lilljeborg as follows : — D- galeaia, a sub-species or 

 variety of D- hyaliyia ; D. ciimllata, with which both D. kahl- 

 bcrg(7isis 2ind Jardmii are sunk as synonyms ; D. cristaia ; and, 

 lastl}', D' lo7igir€77iis. The Ccricdaph7iiidce are equally care- 

 full}' described, and it would seem that the C. qiiadrang^da of 

 most English authors hitherto should be C piilchella, and 

 vice versa, which necessitates the recasting of the nomen- 

 , clature of our recent British lists. But it is among the 

 Bosmi7iidcB especially that I^illjeborg's work has accomplished 

 yeoman's service. Of this perplexing genus a careful and 

 most elaborate survey has been made, and no less than 222 

 figures are given illustrating the characters of nine species 

 and sixteen varieties. A careful revision of old records thus 

 becomes unavoidable, and as a reference to the original 

 specimens is too often impossible, at least with regard to the 

 Irish list, several must drop out pending further research. 

 One interesting feature of these unstable forms appears on 

 compariso of the numerous illustrations given ; namely, the 

 prevalence among the BosTrmtidce, and in a less degree also, 

 among other genera of Cladocera, of a modified habit 

 of seasonal dimorphism. Hitherto we have been familiar 

 with the differences of the sexual characters, as well 

 as that between 5'oung and adult forms ; but it would 

 appear that marked difi"erences of development are also 

 observable between the adults of spring, summer^ and autumn 

 of most species of Bosmina. Further obser^^ations of these 

 phenomena by students of Entomostraca in these countries 

 would be most desirable, in order to insure that local and 

 racial aberrant characters do not confuse the issue, and to test 

 how far this seasonal dimorphism is constant in its efifects in 

 difi"erent climates, and varied environments. For instance, 

 specimens of BosTTzina mixta, var. humilis, sent by the writer to 

 Prof. Lilljeborg, appear to show that our summer adult females 



