BELONGING TO DAPHNIA AND OTHER ALLIED GENERA. 239 



Hob. — Loch Garry, Inverness-shire (Eev. Canon Norman) ; 

 Lough Erne, Ireland (Dr. Creighton). 



On this species, together with several other nearly allied forms, 

 Schoedler founded the genus Hyalodaphnia, of which the only 

 tangible characters are the absence of an "eye-spot" and the 

 produced helmet-shaped head. The value of these distinctions 

 is very doubtful. Some of the helmeted forms, as for instance 

 the following species, D. galeata, have always a small, though 

 distinct, eye-spot, but are in other respects so closely similar to 

 D. Kahlhergensis as to be with difficulty distinguished. Under 

 these circumstance Schoedler's generic name seems of question- 

 able value, and it may even be doubted whether all the mem- 

 bers of the helmeted group should not be looked upon as mere 

 varieties of one very Protean species. This, in fact, is to some 

 extent the view taken by Professor G. 0. Sars, who in a recent 

 work,* while admitting the genus Hyalodaphnia, makes H. hero- 

 linensis and H, Kahlhergensis varieties of H. Jardinii, and with 

 reference to the latter species he makes the interesting observa- 

 tion that the early spring broods have rounded heads without 

 any trace of the crest, which makes its appearance only in the 

 summer broods. Comparing these observations with my outline 

 drawings of various stages of H. Kahlhergensis from Lough Erne 

 it will be seen that there is a somewhat similar progressive varia- 

 tion in the shape of the head from the young to the adult form 

 (figs. 18-21). But it is in the young that we find the acutely- 

 crested head, the high helmet form gradually giving place to the 

 short vertex-spine of the adult. 



The characters, which may be taken as separating D. Kahl- 

 hergensis from D. galeata, are the large size of the head, its 

 wedge-shaped outline, broad at the base or posterior end and 

 gradually tapering to an acute apex, and the absence of an eye- 

 spot : the vertex-spine, which in D. galeata has a ventral bend, 

 is here either straight or slightly bent towards the dorsum. I 

 am confirmed in this view of the distinctness of the two forms 

 by the fact that specimens kindly sent to me by Dr. Creighton 



* Oversigt af Norges Orustaceer — (Cliristiania VideHskalis— Selskabs Forhandlinger, 

 1890). 



