356 ISLAND LIFE part ii 



recognition and correlation. It is therefore only by an 

 actual and careful comparison of authentic specimens that 

 a perfectly reliable list could be drawn up, which would 

 fairly represent the knowledge of the present day. 



It is, however, highly probable that our insular and 

 peculiar conditions do tend to evolve variations in harmony 

 with the local environment, and thus conduce to stamp 

 upon many of our species a recognisably different general 

 facies to that of continental individuals of the same 

 species. The peculiar species are now six in number and 

 embrace — 



Limiicea involuta, Thompson. — A pond snail with a small, polished, 

 amber-coloured shell, found only in a small alpine lake and its inflowing 

 stream on Cromaglaun Mountain, near the Lakes of Killarney. It was 

 discovered in 1838, and has frequently been obtained since in the same 

 locality. It is more properly classed as an aberrant variety of LimTioea 

 peregra, rather than as a distinct species. 



Azeca elongata, Taylor. — A large species of this very limited genus, 

 distinguished by its elongate form and comparatively simple oral armature. 

 It has hitherto only been met with in North Wales and in the Yorkshire 

 Highlands. 



Clausilia cravenensis, Taylor. — A fine species of this group, hitherto 

 confounded with Clausilia dubia, and confined to the uplands of the North 

 of England. 



Paludestrina Jenkins i, Smith. — A small ovoviviparous species, inhabit- 

 ing many localities in England and Ireland, both inland and estuarine. It 

 was discovered some years ago, and first described in 1889. 



Paludestrina taylori, Smith. — A minute species, discovered in the 

 Lancashire canals in 1900. It is very distinct from any known British 

 species, and should be grouped apart from P. jenkinsi. P. taylori is an 

 oviparous species, and, judging from its peculiar and characteristic egg 

 capsules, would be more properly associated with the American group, 

 Amnicola. 



Pisidium hihernicuTn, Westerlund. — An Irish species of this perplexing 

 genus, which has been discriminated by Dr. Westerlund. 



In addition, however, to the six distinct species, 

 enumerated above as not known to occur elsewhere, there 

 are a considerable number of more or less well-marked 

 varieties, which seem to be also peculiar to our islands, 

 and are probably in a great measure a reflex of the 

 characteristic insular environment to which they are 

 subjected. 



The following list of such forms is therefore given, in 

 the hope that it may be useful in calling attention to 

 those varieties which are not yet positively known to occur 



