38 The Irish Naturalist. March, 



nostic characters of P. hihernicum (Cat., p. ii8) can be 

 relied on, in our opinion, to separate it from certain forms 

 of P. iiitidum, P. ohtusalc or P. milium. 



In the report of the Land and Fresh-water Mollusca of 

 the Clare Island Survey, ^ A. W. S. suggested that the present 

 species might be an " American " one : that is to say, 

 that it might belong to the same faunistic group as the 

 s]:)onge Heteromeyenia ryderi — with which it is frequently 

 associated in the West of Ireland — and that its distribution 

 might correspond with that of the plants Eriocaulon septan- 

 gularc, Naias flexilis and Spiranthes Romanzoffiana, which 

 outside North America live only in a few stations in N.W. 

 Europe. The occurrence of P. hihernicum in Wales, England, 

 Norway and Sweden suggests, however, that it is probably 

 a wddely distributed Palaearctic form. Recently we have 

 acquired a collection of Pisidia received by Mr. J. R. le 

 B. Tomhn from Mr. Bryant Walker of U.S.A. — all of which 

 are said to have been identified by Dr. Sterki. Amongst 

 these are shells labelled " P. mediamim Sterki " (Plate II., 

 figs. I and 2), and others " P. mediamim, var. minnta 

 Sterki," which bear a remarkable resemblance to forms of 

 P. hihernicum. To sav that thev are P. hihernicum would 

 be impossible in such a group as the Pisidia, but had these 

 shells been found in Ireland, we think that they would have 

 been referred without doubt to that species. 



The only fossil examples of P. hihernicum which we have 

 seen come from Irish shell-marls and are of post-Glacial 

 age ; but it will not surprise us if the species proves to have 

 been overlooked in some of the pre-Glacial deposits in 

 England or on the continent. 



We have to thank numerous workers for assistance in 

 accumulating the information given in the following lists : 

 Messrs. P. T. Deakin, N. C;. Hadden, H. C. Huggins, J. W. 

 Jackson, J. N. Milne, J. E. Cooper (for allowing us to 

 examine his large series of shells named " P. nitidum " by 

 Mr. B. B. Woodward, in which were detected two sets of 



* Proceedings I\. J. Acad., vol. jcxxi-, part 23. 



