g 2 [Proc. B.N.F.C, 



connected with the Irish fauna and the geographical evolution of 

 Ireland. It has been known for many years past that in a certain 

 measure the west coast of Ireland forms the meeting ground of 

 the southern and northern marine fauna. As in western counties 

 we observe also in the adjoining marine area that curious mingling 

 of southern and northern animals. Some northern forms of life 

 extend their range much further south than Ireland, while a few 

 southern species have succeeded in penetrating to Scotland and 

 even beyond it. Among the latter some have attained the 

 extreme northern boundaries of Scotland and have then turned 

 south-eastward skirting along the east coast of Scotland. Instead 

 of taking the much shorter route through the Straits of Dover we 

 find that these southern forms have preferred the circuitous way 

 along the west coast of Ireland and Scotland to reach their 

 destination. Several instances might be quoted of species 

 possessing such a distribution, but I need not go into further 

 particulars. I will give you just one example of a typically 

 southern species which has spread as far as the north-west coast 

 of Ireland, namely, the Purple Sea-Urchin, Strongylocenirotus 

 lividus. The Purple Sea-Urchin inhabits the Mediterranean, it 

 occurs along the west coast of Portugal, Spain, and France, and 

 re-appears across the English Channel on the coast of Cornwall 

 and Devonshire, and then again on the coasts between Cork and 

 Donegal. It is quite absent from the east coast of Ireland and 

 all other parts of Great Britain, except those mentioned. Instances 

 of that kind — and there are many — with that curiously disjointed 

 or discontinuous distribution indicate that we have to deal with' 

 an old route of dispersal along a former continuous coast-line. 

 We can best explain their distribution by the supposition that 

 they spread northward at a time when the English Channel was 

 closed and when a continuous coast-line extended from France to 

 the west of Ireland. 



This completes the short resume of one of the most absorbing 

 branches of the subject, on which I have been asked to address 



