120 The Irish Naturalist. Aug.-Sept., 



previously called " L. involuta " ; a much more active 

 larger-shelled one, which has a higher spire and appears 

 glistening whitish in the water, and from its extreme tenuity 

 of shell may, for purposes of reference, be called " L. 

 praetemns," and a usually strongly spired, rougher, still 

 thicker-shelled group which appears brown or dark yellow 

 in the water, to which I shall refer as " L. pereger." The 

 characters in these groups are not constant, " L. involuta " 

 sometimes has a spire, and " L. praetenuis " in one locality 

 is almost invariably intorted, though differing in no other 

 respect from the shell described as that species from Lough 

 Nagarriva. 



I carefully examined each lake but on no occasion did 

 I find L. praetenuis or L. involuta co-existing with L. pereger 

 or each other, and as none of these three molluscs co-exist 

 in any other locality I am of the opinion that L. involuta 

 and L. praetenuis are simply extreme forms of a lacustrine 

 race of L. pereger, though this may possibly prove to be a 

 distinct species from the L. pereger found in streams and 

 ditches. My idea is, I think, borne out by the fact that, 

 though all the lakes appear of an exactly similar character, 

 there are nevertheless some factors connected with each of 

 them causing variation, as I am assured by the local 

 fishermen that each contains a distinct race of trout ; 

 and the fish I had an opportunity of examining from 

 five lakes bore out the statement. The fish from Lough 

 Nambrack, pale green, oval, with a very few small black 

 and pink spots, made a striking contrast with the thick 

 copper-red ones from Red Trout Lough, only half a mile 

 away ; the latter being covered with large black and 

 flaming crimson spots. If any collector who is also a fly- 

 fisherman should visit the neighbourhood it might prove 

 of interest to catch and compare the fish from each lake, 

 possibl}' similar races of trout would be found to inhabit 

 the L. praetenuis tarns, and corresponding races the localities 

 for L. pereger and L. involuta. 



Very few of the Caha lakes are named on the one-inch 

 ordnance map, but I kept a note-book as I collected in 

 which I marked the lakes A, B, C, etc., as in the 

 accompanying map. Although the lakes themselves are 



