1903- Kan:^. — Irish Fresh-water E7itomostraca. 213 



correspond to vernal Swedish examples in the comparative 

 shortness of their rostra. Examples from L. Erne are character- 

 ised by a remarkable absence of development in the spinal 

 processes at the infero-posteal angle of the shell valves, indeed 

 in man}^ instances the angle is almost obtuse, as sometimes 

 obtains in examples of B. coregoiii ; but examples from 

 Eough Conn are like the Swedish type. And this leads me to 

 observe that the differential character relied on b}^ Lilljeborg 

 between these two species seems a rather trivial one, though it 

 may nevertheless be quite reliable. It is the absence in the 

 latter species of the seta which is to be found on the shell 

 valves of most other s^^ecies near the infero-posteal angle ; but 

 which is almost rudimentary and obsolete though still trace- 

 able, in the closely allied species B. mixta. Of the absence of 

 the seta in the Scottish I^. Maben examples (which till lately 

 was the only known British locality), I am assured by that 

 careful and accurate observer, Mr. Scourfield. But specimens 

 oi Bosnmia mixta ^\\\q\\ had sUvStained rough treatment and 

 lost the vestiges of the seta, would conform otherwise very 

 closely to B. coregoni. Now, it is interesting to find that in a 

 certain part of L- Erne, specimens oi Bosviina were taken, the 

 greater part of which wxre referable to B. mixta, and a few to 

 B. co7'cgoni. If the identification had rested on any lesser 

 authority than that of Prof. Eilljeborg himself, doubts might 

 have been thrown upon its accuracy. The fact of both species 

 occurring together is remarkable. It is unfortunate, too, that 

 in my gatherings at I^. Oughter very few specimens of ^. mixta 

 were taken, and those irot very good ones, the test being some- 

 what discoloured, so rendering examination diflicult. It is to 

 be hoped that having such a valuable text-book to consult, the 

 various questions in dispute, and doubtful identifications 

 which hitherto obstructed students of this group will cease to 

 hinder progress, and that before many years we shall reap a 

 rich harvest of valuable facts from our numerous and diver- 

 sified Irish inland waters. But, although the occurrence of 

 northern species with us, such as these, two Bosminidse and 

 Bythotrephes C(f^^r.?//c>■;;^^V, is of extraordinary interest, as offering 

 in conjunction with other branches of natural history conver- 

 gent testimony as to the genesis of a portion at any rate of 



