Freshwater Mollusca of Ireland. 



201 



Those acquainted with Mr. Gray's catalogue, will perceive that 

 four of the species it contains are omitted, — the three Conovuli and 

 Dreissena polymorpha, which is an introduced and not an indigenous 

 species. Of the twenty- eight species which Great Britain and her 

 islands would thus seem to possess over Ireland, it must be stated 

 that Turton has enumerated four as Irish, viz. Helix lapicida, H. 

 Cantiana, Limneus glutinosus, and Unio pictorum ; but as he some- 

 times introduced species without sufficient reason, and as these are 

 unknown to my correspondents and to myself, they are omitted — 

 if correctly placed in our fauna by that author they will in all pro- 

 bability yet be found. Paludina achatina is included by Mr. Gray 

 (Man. p. 34), but on what authority he could not recollect when I 

 lately saw him at the British Museum. I have been told of the 

 occurrence of a few species, which, in the absence of sufficient proof, 

 are not included in the catalogue. Two of the Helices, — H. aperta 

 and H. revelata, — have been introduced to the British list from 

 Guernsey. 



It appears from the foregoing catalogue, that four generic forms 

 indigenous to England have not been found in Ireland, Assiminea, 

 Azeca, Segmentina, and Unio ; these comprise seven species, if four 

 Unios be admitted as distinct. 



It may be desirable to dwell for a moment on the distribution of 

 those species in Great Britain which have not been found in Ireland. 

 Of these, Assiminea Gray ana is confined to the south-east of Eng- 

 land, and is " seldom found out of the reach of brackish water." 

 Paludina achatina and P. ventricosa are not generally distributed in 

 England, and are unknown in Scotland*. Limax brunneus has been 

 observed only at Newcastle and Berwick. Helix aperta (H. nati- 

 coides, Drap.) and H. revelata have not been found in Great Britain, 

 but only in the island of Guernsey. H. obvoluta would seem to be 

 confined to Hampshire, as H. limbata is to one quarter of the neigh- 

 bourhood of London. H. Pomatia is found chiefly in the chalk di- 

 stricts of the south of England. H. Cantiana now occurs from the 

 south to Newcastle-upon-Tyne, but is believed to have been intro- 

 duced to this northern locality with ballast. H. Carthusiana (H. 

 Carthusianella, Drap.), is confined to the south-east ; H. lapicida 

 prevails in the south, and along the eastern portion of England — 

 not one of the above Helices is found in Scotland. Succinea oblonga 

 has been obtained only in three localities, North Devon, and in the 

 neighbourhood of Swansea and Glasgow. Bulimus Lackamensis is 

 a south of England species — to Scotland it is unknown. Azeca 

 tridens is widely distributed over England, and is also indigenous to 

 the south of Scotland. Pupa Juniperi would appear to be chiefly 

 confined to the south of England and South Wales. Vertigo cylin- 

 drica is very rare, and has been found but in three British localities — . 

 the neighbourhood of Bristol, of Edinburgh, and in the isle of Skye. 

 Vertigo alpestris has been procured only in two stations — in Lanca- 



* A manuscript catalogue of the land and freshwater mollusca of Scot- 

 land, favoured me by my friend Edward Forbes, Esq. is my authority. 



