52 



ON THE PISIDIUM GASSIE8IANUM OF DUPUY. 

 By A. W. Stelfox, M.R.I.A. 



Eead 13th January, 1922. 



By the majority of authors the name Pisidium gassiesianum of 

 Dupuy has been applied to the species we now know as P. milium, 

 Held, probably because of the excellent figure in Baudon's "Essai " (5), 

 these authors apparently not contemplating the possibility that 

 Baudon had figured a wrong species under this name. 



Yet if the figure of Dupuy's P. gassiesianum, 1852, (3) be compared 

 with P. milium. Held, discrepancies between the two will be obvious. 

 Though often puzzled by these facts, it is only recently that I gave 

 any thought to the matter, and it then became apparent that the 

 P. gassiesianum oiDu-puy, February, 1849, (1) had nothing to do with 

 the P. gassiesianum of Gassies, March, 184:9. (2) Reference to the 

 Journal de Conchyliologie at once confirmed this conclusion and 

 explained how the mistake had arisen. 



Briefly this is my reading of the story. Dupuy visited Glassies in 

 1848 and the two spent considerable time in the field together. 

 Gassies took Dupuy to Chantilly, and showed him a Pisidium, which 

 he proposed to name P. limosum and Dupuy agreed that it was an 

 undescribed species. Together they discovered at Ratier another 

 Pisidium, which both at the time agreed was also new, but which 

 Dupuy must subsequently have decided was not a new species. 

 Dupuy returned home and reversed the labels attached to the two 

 species (or as Gassies suggests, permitted them to be reversed by 

 the printer) ; and so when he suggested to Gassies, in a letter, 

 that he proposed to describe the new species from Ratier as 

 P. gassiesianum, Gassies naturally did not understand that Dupuy 

 referred to his own proposed P. limosum from Chantilly and vice 

 versa. During this time Gassies also was preparing a paper which 

 appeared a few weeks after Dupuy's and before Gassies had 

 discovered Dupuy's"error. 



Consequently the P. gassiesianum of Dupuy, 1849, is a synonym 

 of the P. limosum of Gassies, 1849, and takes precedence. This 

 synonymy is correctly given by Dupuy in 1852. When Baudon 

 published his Essai (1857) he allowed himself to be persuaded 

 by Gassies (4) to apply the specific name gassiesianum to the 

 p. gassiesianum of Gassies, and not to that of Dupuy. Subsequently 

 Baudon under the influence of Normand, confessed his error ; (6) 

 yet one finds authors who refer to the P. gassiesianum, Dupuy, as 

 a synonym of P. milium. Held. 



Recently I have been enabled to examine authentic — " ex 

 auctore "■ — examples of P. limosum, Gassies (i.e. P. gassiesianum, 

 Dupuy), preserved in the Museum at Bordeaux. These prove to 

 belong to the species brought forward as British in 1908 by Mr. B. B. 



