130 REPORT— 1839. 



inland. The number of varieties oi Helix nemoralis and hor- 

 tensis found on sea-banks is much greater than when those spe- 

 cies are gathered inland, and their colouring generally more 

 vivid. When Helix aspersa is found plentifully near the sea, 

 as in the Isle of Man, Ayrshire, and other places, the banding 

 is much more distinct, and the ground colour brighter. Most 

 species found near the sea vary very much, and many spurious 

 species have been made in consequence, as we see in the cases 

 of Helix striata, Helix variabilis, and Bulimus acutus. The 

 last would appear to be confined in Britain to sea-banks, 

 and to those of the western coast only. This does not apply 

 to Ireland, where it is found both on the eastern and western 

 coasts, and also inland. The difference between the faunas of 

 the eastern and western coasts of England is very remarkable. 

 Rivers influence the fauna of a district by the introduction of 

 species not indigenous. Many of our local lists are swelled by 

 the names of species collected from the rejectamenta of neigh- 

 bouring streams. A stream flowing from a mountain-range into 

 a plain will convey many species into the latter, which are pro- 

 perly inhabitants of the former. In Britain, where there is no 

 positive influence of elevation, this is of comparatively little con- 

 sequence ; but the case is different on the continent, where 

 large rivers, such as the Rhine and Danube, convey the in- 

 habitants of the Alps into the plains of Germany. Even 

 in our own country such rivers as the Thames and Severn 

 are likely to give rise to many fallacies as regards the local 

 distribution of a species. Man's agency may materially affect 

 a fauna, and has affected that of Britain. Bulimus decollatus, 

 Bulimus clavulus, Clausilia solida, and Testacella Maugei, 

 have been introduced into the British Hsts by such means. In 

 the cases of the above-mentioned species the carriage of plants 

 from other countries has been the medium. It has been as- 

 serted that Helix pomatia was first introduced into Britain for 

 purposes of food ; but there are good grounds for regarding it 

 as an aboriginal native. The thriving of such introduced 

 species must depend on the locahties to which they are trans- 

 ported ; and should a species, the distribution of which is 

 mainly influenced by geological causes, be introduced on a 

 soil similar to that of its native habitat, it is especially likely 

 to thrive and multiply. Species may be introduced into a local 

 fauna by means of ballast. On the banks of the Frith of 

 Forth we find numerous dead shells of Paludina vivipara and 

 impura, and Neritina fluviatilis, none of which inhabit the 

 district, but which have been conveyed thither in ballast, 

 thrown into the water, and again cast up on the shore. Land 



