10 The Irish Naturalist. January, 



not from " Thomond " there would be a strong tempta- 

 tion for the record-hunter to chivy it over the border 

 before capturing it. But such deplorable chicanery could 

 not have occurred to the mind of Mr. Adams, for he says 

 " Species obtained by shore-collecting belong {naturally 

 enough) to the count}^ on whose shores they are collected." 

 Nor, apparently, have the vagaries of " low-water mark," 

 as a territorial boundary, troubled him. 



But these minor absurdities do not constitute the chief 

 objection to such ready-made faunistic and floristic 

 divisions of a country. They are fundamentally wrong, 

 insomuch as they precede a knowledge of distribution, 

 instead of being based on it. If they are to have any 

 value they must represent the observed limitations of 

 species or groups of species. These distributional limita- 

 tions njust be correlated with the habits and life-histories 

 of the species, and those factors in the environment which 

 prevent their further dispersal. It will then be obvious 

 (as it is now) that each species has its own peculiar dis- 

 tribution, and onh' two divisions will be necessary to 

 express it, one in which it occurs, and one from which 

 it is absent. 



In reading papers on the geographical distribution of 

 the marine organisms occurring in various localities in the 

 British Isles, one often meets such a statement as this : 

 " The fauna (or flora) of our area is a remarkable mixture 

 of northern and southern forms." This announcement is 

 always made with the air of imparting an important dis- 

 cover}/, and is usually accompanied by a mass of statistical 

 information. For instance, the following sentence occurs 

 in a recently published paper : — " A study of this table 

 reveals the interesting fact that the marine fauna of the 

 west of Ireland, as far as these orders of Crustacea are 

 concerned, is a blending of northern forms with southern 

 species from the Mediterranean, the latter element some- 

 what preponderating." It is difficult to see what alternative 

 the writer considered possible. Owing to the usually re- 

 stricted bathy metrical range of marine organisms, and the 

 general north-south trend of the European coast, the 

 fauna could hardly be a mixture of eastern and western 



