14 ., Proceedings of the Royal Irish Academy. 



consequence, Ulster being the coldest of the four, while Munster is the 

 warmest. With regard to other subdivisions of the country, obviously the 

 labour of indicating the distribution of Alg^e in each of the forty divisions of 

 Praeger's "Topographical Botany" would be very great. The twelve divisions 

 of " Cybele Hibernica " are so arranged that some are entirely inland, while 

 others liave a long coast-line ; and this renders a comparison betw^een the 

 flora of two such divisions impracticable. The twelve divisions, moreover, 

 are such that some occur partly in one province, partly in another. 



Holmes and Batters, in their " List of the British Marine Alg^," in 1890, 

 divided the Irish coast-line into five parts — an arrangement which was 

 adopted subsequently in "Irish Phaeophyce^e" — but Batters, in his "Catalogue 

 of British Marine Algse" in 1902, abandons these divisions. Zoologists 

 divide the Irish coast-line into six regions, while, on the other hand, the 

 " Fishery Districts " are twenty-one in number, and vary extremely in 

 length. For these reasons then, I have fallen back on the province as the 

 unit of area. 



Explanatory Bemarks. — The freshwater species are tabulated in a separate 

 series from the marine, as the biological division into these two groups is 

 well recognized, and is more convenient for reference. The genera under 

 each main group of Algte are arranged in alphabetical order, and the same 

 arrangement has been adopted for the species of each genus. Had the genera 

 and species been grouped according to their affinities, the labour of finding 

 any particular species would have been enormously increased unless an Index 

 had been added. The importance of this saving of time will be realized, 

 when it is stated that the single genus Cosmarium contains 170 species. 

 The distribution of each species is indicated by the letters M, L, C, U, being 

 the first letters of the names of the four provinces. 



As regards the limits of a species, authorities differ considerably, some 

 investigators considering a so-called new species as merely a variety of some 

 already existing species. To secure uniformity in this respect, I have adopted 

 for the most part the arrangement and nomenclature of De Toni's great 

 work, " Sylloge Algarum " (1889-1907). 



Dotibtful Sjyecies.— In a few cases a species has been mentioned in some 

 old record as occurring in Ireland, and the description is so incomplete that 

 it is difficult to identify it as a synonym of a well-authenticated species 

 bearing a modern name. In other cases there is a doubt as to whether a 

 specimen was correctly identified. It is a matter of opinion whether such 

 should be included in this paper. On the whole, I have decided to include 

 them, but in a sort of appendix at the end of each group, in the hope that 

 some light may hereafter be thrown upon them by future observers. 



