i8 



The Irish Naturalist, 



February, 



I. 



2. 



Canthocamptus pygmaeus. 

 Candona Candida. 

 Cypria ophthalmica. 



Canthocamptus lucidulus. 

 Cyclops fimhriatus. 

 Chydorus sphaericus. 



Brackish pools by the estuary were found to be rich in 

 Entomostraca, among which the following are worth 

 mention : — 



Halicy clops aequoreus Fisch. 

 Nitocra typica Boeck. 

 . Nitocra spinipes Boeck. 

 Mesochra rapiens Schmeil. 

 Tachidius littoralis Poppe. 



Nitocra typica also occurred in the estuary itself. It 

 appears to be a rather rare species preferring more saline 

 water than A^. spinipes, although sometimes (as on this 

 occasion) living in company with it. Mesochra rapiens 

 {—M. hirticornis Scott) has, so far, only been found in one 

 locality in Ireland— Clare Island (Scourfield) . It is 

 characteristic of water of very low salinity, and occurs 

 even in perfectly fresh water. I was not able to analyse 

 the water of these Malahide pools, but, to judge by the 

 situation and nature of the fauna, the salinity must have 

 been high — at least 12 grms. chlorine per litre. 



In a small trickle of fresh water draining into the 

 estuary was found, in company with Nitocra spinipes, a 

 variety of Cyclops languidus which differs so much from 

 the type as to constitute apparently a. distinct species. 

 This form has only 11 joints in the first antenna, and differs 

 from C. languidus in the form of the swimiming legs, in 

 which the terminal joints are scarcely longer than broad, 

 while the terminal spines of the inner branch of the fourth 

 foot are of very unequal length. There are a number of 

 forms of Cyclops closely related to C languidus, to several 

 of which specific names have been attached, and a careful 

 revision of these forms is much needed. I am acquainted 

 with two of these varieties in addition to that above 

 mentioned, neither of which seems to agree with published 

 descriptions, and must defer a detailed description of these 

 forms to a future occasion. 



