202 Mr. W. Thompson's Catalogue of the Land and 



shire and Northumberland. Clausilia biplicata is confined to the 

 south of England ; C. Rolphii to one or two localities in the south- 

 east; C. dubia is, I believe, as yet known only to the north of England. 

 Limneus glutinosus, Cyclostoma elegans, and Cyclas vivicola, are some- 

 what widely diffused in England, but are unknown to Scotland. 

 Segmentina lineata is noticed by Mr. Gray as a south of England 

 species, but is included in Mr. Forbes's list of Scottish mollusca. 

 The genus Unio, as now restricted, becomes rare towards the north 

 of England, and is not found in Scotland. The species of land and 

 freshwater mollusca indigenous to Ireland, assimilate with those of 

 Scotland much more nearly than those of England. About one- 

 half of the species in which Ireland is deficient prevail chiefly in the 

 portion of England which lies to the south of Ireland. 



I should, perhaps, in conclusion, have ventured to offer some re- 

 marks on the causes which appear to influence the distribution of 

 our Irish species, but the views put forward in my friend Mr. Forbes's 

 excellent ' Report of the Distribution of Pulmoniferous Mollusca in 

 the British Isles,' published in the volume for 1839 of the Report 

 of the British Association for the Advancement of Science, renders 

 unnecessary anything I could say upon the subject. 



APPENDIX. 



My notice of the genera Avion and Limax at the beginning of this 

 article is so scanty, that I here avail myself of very full and inter- 

 esting observations on the species appertaining to them, since fa- 

 voured me by Mr. Clarke, who much more than any one in this 

 country has bestowed attention on the subject. 



Avion atev. 



A. Empiricorum, Ferus., t. 2. 



La Bergerie, Queen's county ; county Galway. Too abundant in 

 both places, varying from the light yellow-coloured variety through 

 all the shades of brown or ochre to deep black. The brown variety 

 seems to predominate in Killereran (county Galway) meadows and 

 woods, but I have repeatedly observed the two colours indiscrimi- 

 nately mixed together in precisely the same localities, both in fields 

 and gardens. The yellow, which I have never taken of the full 

 size, is mostly confined to the decaying pieces of wood found among 

 damp moss. I have not noticed the variety with the scarlet foot, as 

 in fig. 2. t. 2. Fer. I have seen two individuals busily engaged de- 

 vouring a snail (H. aspevsa), both their heads being introduced 

 within the shell : the snail appeared to be fresh killed. 



Avion hovtensis. 



A. des Jardin, Ferus., t. 2. f. 4—6. 

 Var. a. f. 6. Fer. 

 Var. fl. Pfeiffer. 



La Bergerie and county Galway. By no means scarce. Ferussac's 

 figures agree accurately with mine, but are represented of larger 

 dimensions than any I have seen. I have taken the young of a 

 very minute size with the orange foot, and the colours equally as 



