430 ON ILTOPSYLLTJS COKIACEUS AND OTHER CETJSTACEA. 



During a recent visit to Alnmouth, however, I was fortunate 

 enough to meet with Ilyopsyllus in the mud of the salt-marshes 

 near the mouth of the Aln. It is not confined to one bit of the 

 river but may be found I think almost anywhere on the surface 

 of the tidal mud, though probably restricted pretty much to the 

 belt just below high water mark. Most of my specimens were 

 obtained in the extensive backwater on the south side of the 

 river, in a patch of reeds growing at the extreme edge. 

 The little creature is by no means abundant and one has to col- 

 lect a good deal to secure a very few examples. In the very 

 first gathering which I made there I noticed, on examining my 

 captures with a powerful hand-lens, a minute moving speck 

 of a brilliant red colour, so brilliant that one must resort to the 

 terms of the jeweller adequately to describe it ; ruby is indeed 

 pale by comparison, I at once recognized that I had chanced, 

 for the third time upon Ilyopsyllus, and a few more visits to the 

 place enabled me to secure specimens, few indeed, but sufficient 

 for further investigation of its structure. The creature is very 

 small and its extremely tough exo-skeleton makes its dissection 

 a matter of difficulty : moreover it is exti'emely opaque, and I 

 found it impossible to get rid of the colour. I tried steeping 

 specimens in solution of Potash and in Sulphurous Acid, but 

 without ejGfect. Perhaps a more prolonged immersion in some 

 such medium might give better results. Still, I have succeeded, 

 I tliink, in making out most if not all of the structural details, 

 which are in many respects of great interest. It may be noted 

 that Mr. T. Scott has described in a paper on the Entomostraca 

 of the Gulf of Guinea,*' a very closely allied (perhaps really the 

 same) species — Ilyopsyllus affinis — which was taken amongst 

 Confervse in a lagoon at Sao Thome Island. The very minute 

 mouth organs of this species are illustrated in detail, but do 

 not seem altogether to agree with those which I have been able 

 to observe in /. coriaceus. Unfortunately no further specimens 

 of /. affinis are available for comparison and the original dis- 



* Report on Entomostraca from the Gulf of Guinea by Tliomas Scott, F.L.S., Natu- 

 ralist to the Fishery Board for Scotland (Trans. Linn. Soc, Lond.. 2nd series, Zoologry, 

 Vol. vi., Part 1, 1894). 



