SIKLFOX : I'lSiniUM FAUNA OK THE GRAND JUNCTION CANAL. 293 



ties,' and these are the more interesting as no less than four of them 

 appear to be included in Mr. Woodward's Catalogue, as forms of his 

 P. supinum? In making this statement I am not relying altogether 

 on Mr. Woodward's figures, but upon specimens on which records 

 given in his Catalogue are founded. Thus the form of P. supinum 

 most common in the canal is that referred to by Mr. Woodward as 

 the very triangular form of P. supinufti ; some of what he regards as 

 the young of this are, in my opinion, the thickened form of P. par- 

 vulum ; whilst my P. nitidum var. crassa is styled by him "/*. supinum 

 (ovate form)," and is figured in his Catalogue, plate xxv., fig. lob. 

 Finally, what Mr. Woodward refers to as the inappendiculate form of 

 P. supinum would appear to be the shell I here describe as P. cascr- 

 tanum var. ponderosa:' 



Systematic Notes. 



P. amnicum (Miiller). Plate 7, figs. 35-39. 



The form which lives in the canal is somewhat thickened and 

 generally strongly striate or almost ribbed. 



P. casertanum (Poli) B. B. Woodward. Plate 7, figs. 24-34. 



Numerous forms live in the canal. Three of these differ so mark- 

 edly that at first I was almost inclined to look upon them as three 

 distinct species, especially as in several gatherings forwarded to me 

 alive by Mr. Oldham all three occurred in association."' This pheno- 

 menon may possibly be explained by the fact that the trafific on the 

 canal stirs up the mud, and thus forms formerly living under different 

 conditions of environment come to be found in association, just as 

 they would be brought together in rivers during floods. Or, as Mr. 



T For some time Mr. Phillips has held that P. supinum is this missing, thickened form of 

 F. henslo-cvanuin, corresponding with my varieties crassa of P. nitidum and ponderosa of P. 

 casertanum, which as Mr. Phillips so truly points out, are always to be met with where /-". 

 supinum occurs. With Mr. Phillips's view I am in full agreement, but it is too big a matter to 

 be discussed at length in the present paper. I may say, however, that the only alternative I 

 can see to regarding P. supinum as a variety or perhaps sub-species of P. henslowanum is to 

 raise the thickened forms of all the other species to specific rank also. It may be stated that 

 Mr. Phillips's suggestion is not new, since Malm regarded specimens he had received from the 

 original habitat for Schmidt's species — the River Panke, near Berlin — as being at most a thick- 

 shelled, local race of P. hetisloiuanum. 



2 See Oldham on the various forms of Mr. Woodward's P. supinum, Journ. of Conch., 

 vol. xiii., p. 53. 



3 Since this paper was read before the Society I have received, by the kindness of the 

 author, a copy of Herr C. M. Steenberg's Monograph on the Mollusca of the Fure Lake in 

 Denmark. From this it would appear that a similar form oi casertanum has been mistaken for 

 P. supinum in his country, as in this. 



4 111 this connexion it is interesting to nute that Herr Steenberg records {_loc. cit.) three 

 forms of this species from the Fure Lake in Denmark — a typical foripj a thickened triangular 

 form, and one he refers to as " f . lacustris 13. B. Woodward." 



