ON BRITISH PULMONIFEROUS MOLLUSCA. 137 



coast of Britain. Acme lineata extends to Preston, the most 

 northern hmit, by the way, of Paludina vivipara. Pupa al- 

 pestris was first observed in Lancashire. In the slaty districts 

 of North Wales and Cumberland the number of species is less 

 than in other parts of the district. In the Isle of Man, which 

 I append to this province, we find but a small list of species. 

 Plcuiorbis marginatus is altogether wanting in that island. 

 The marine influence is evident there and in North Wales. 

 Helix ericetorum is, in this province, a sea-side species. On 

 the whole, this is the part of England least favourable to the 

 multiplication of species, and where the influence of climate is 

 either negative or neutralized by geological structure or ma- 

 rine influence. 



Districts VI. and VII. — In Ireland we see the climatal influ- 

 ence predominating in the extreme south, but counteracted by 

 geological structure, the geological influence predominating in 

 the extreme north, but counteracted by the negative influence of 

 climate ; whilst the greater part of the intermediate districts pre- 

 sents the influence of carboniferous strata, modified by peculia- 

 rities of climate. The presence of Testacellus in the south is 

 proof positive of climatal influence, as also is that of Helix 

 pisana in the neighbourhood of Dublin. Generally speaking, 

 however, the Pulmonifera of Ireland correspond to those of 

 the extreme north of England and the south-west of Scotland. 

 Ireland presents us with one aquatic species peculiar to it, the 

 Limneus involutus, hitherto unobserved in any other part of the 

 world, and by far the most remarkable of all the species of its 

 genus. The number of true species of Pulmonifera found in 

 Ireland is 75 ; thus exceeding Scotland by four, but falling 20 

 short of England. On the distribution of these, my friend Mr. 

 Thompson, of Belfast, has favoured me with the following 

 notes, as well as all the other information I possess on this divi- 

 sion of the Irish Fauna. The difference in number between the 

 species found on the north and south of Ireland is trivial as 

 far as known, and cannot be stated with certainty. Of species 

 found in the more southern half of Ireland, and not in the 

 north, the following may be mentioned : Testacellus haliotoi- 

 deus (var. scutulum), at Youghal ; Helix globularis, Helix 

 striata, Achatina acicula, and Limneus involutus. Clausilia 

 bidens, which has been obtained in Cavan and Fermanagh, and 

 Planorbis Icevis, common to Down and Antrim, have not been 

 observed in the south. Helix pisana is only found in the 

 county of Meath. Planorbis cor?ieus is found only towards the 

 centre (as to latitude) of Ireland. The chalk district of the 

 north seems to have little influence on the species of the Pul- 



