1869] Harvey's Water- Snail. 2 1 1 



through the unsafe practice which its own discoverer had 

 always condemned,* of judging" generic characters by the 

 shell ; and had been grouped with its supposed near rela- 

 tion, L. glutinosa, in the sub-genus Amphipeplea. The 

 similarity of shell on which this grouping was based is 

 certainly close, for Harvey himself relates that when he 

 first found his shell he thought he was gathering L. 

 glutinosa. 



Before returning to Dublin, Mr. More now visited 

 Lough Crincaum, and made a successful search for " Har- 

 vey's water-snail," of which he collected a number of live 

 specimens to be kept under observation in a glass bowl. 

 Then after some ten days' study of his captives, he was 

 in a position to write the first published description of 

 " the animal of Limnaea involuta." In doing so he demo- 

 lished the idea of its belonging to the sub-genus Amphi- 

 peplea, in which (as the name denotes) part of the mantle 

 of the mollusc, when protruded, is thrown back so as to 

 enfold the outside of the shell. He found " no appearance 

 of any outer lobe or expansion of the animal covering the 

 outside of the shell as in Amphipeplea glutinosa. The 

 mantle in Limnsea involuta is not developed to any greater 

 extent than in any other allied species, such as L. peregra 

 and L. auricularia ; and the external surface of the shell 

 remains at all times uncovered, whether the animal is ex- 

 panded or not."f The question may seem a simple one 

 to have remained for so many years unsettled, but the 

 observation required some patience. 



For years afterwards, when visiting Killarney, where 

 he went nearly every spring, he made a point of returning 

 to the little lake on Cromaglaun, and invariably carried 

 back to his room in the museum a few live specimens of 

 Limnsea involuta, whose affinity with the species peregra 



* In a letter, dated January, 1831, a year before his discovery of Limnaea 

 involuta, Harvey wrote : " I do not feel competent to write on the genera or 

 families of univalve shells, as I know so few of their animals; and from those I 

 do know I am convinced that no system in accordance with nature can be estab- 

 lished, when the generic characters are taken exclusively from the shells." The 

 case of his own water-snail conspicuously illustrates the wisdom of this remark. 



t "Annals of Natural History " (4), vol. iv., p. 46. 



P 2 



