218 Proceedings of the Roijal Irish Academij. 



the family Eimicidae, the British species of which have mostly a southern 

 distribution, there are 14 species recorded from Plymouth, and only one 

 species from Dublin Bay. The Annelid fauna of Dublin Bay diflers markedly 

 from that of the west coast of Ireland, which in its turn closely resembles 

 that of PljTnouth. 



The chief geographical feature of the Annelid fauna of Dublin Bay is its 

 generalized character. Most of the species have a wide distribution, and are 

 to be found in many parts of the British Isles and the adjacent coasts of 

 Europe. One of its most interesting components is a group of species which 

 have a distinctly northern or Ai-ctic distribution. Of these the species 

 Prionospio Slccnstrupii, Malnigi'en, ma}' be taken as an example. Its only 

 Britisli habitat so far known is a little north of Balbriggan, where a single 

 specimen was taken. It is a very inconspicuous little animal, and probably 

 occurs on the west coast of Scotland. Elsewhere it is found in Norway, 

 Iceland, Greenland, and Eastern Nortli America. Its distribution is t}^iical 

 of a group of sjiecies wliich is found in the northern part of the Irish Sea, 

 and which seldom extends so far south as Dublin. There is also a small 

 group of species having a distinctly southern distribution. Of these Lepi- 

 donotns clavfi, Mont., may l>e taken as a type. It is found on tlie west coast 

 of Scotland, the west and north-cast coasts of Ireland, tiie English Channel, 

 Medit«n-anean, and Canaries. It seems probable, from the distribution of 

 this group round tlio west and north of Ireland, and frequently on the west 

 of Scotland, that these southern species reached the Irish Sea round the north 

 of Ireland, and not round the south. 



This generalized character of the Dublin Bay fauna may be easily accoimted 

 for on geological considerations. The east coast of Ireland in comparatively 

 I'ccent times did not exist, as Ireland was joined on to England. As the land 

 gradually sank, and the Irish Sea was formed, tiie marine fauna immigrated 

 into tlie new area, and in consequence we find the fauna composed chiefly of 

 sjiecies which are common in tlie adjacent seas. Its arrival has probably 

 l)een so recent that the processes of variation, selection, and extinction have 

 not had suliicient time to dilVerentiate the fauna from that of the neighbouring 

 districts. 



Ill order to put these theories on a souiul basis, a much more complete 

 knowledge of the distiibution of the littoral and shallow-water faiuia of the 

 r.ritiah Isles is necessaiy, and especially that of the north and south coasts of 

 Ireland, al>out whicli we know practically nothing. Another factor in the 

 sriliitiiiii fif iliis ]irolileni would 1k> a knowledge of tlie prevailing currents in 

 tlie Irish S«i, by means of wliich tlic pelagic larvae of tlie Annelids would be 

 earned horn place to place. Many species have a very restricted local range ; 



