212 BRITISH CARBONIFEROUS BRACHIOPODA. 



Before proceeding further it may be as well that we should inquire into what has 

 led to this extraordinary multiplying of species? Has it not been caused by the 

 uncertainty and difference in opinion that exists among naturalists with reference to what 

 should constitute genera and species, as well as by the ignorance and precipitation with 

 which we are so often apt to consider new, what may not be known to us ? 



Deshayes in his paper on the distribution of Acephalous Mollusca in the tertiary basin 

 of Paris, observes: — "For us the genus is a creation of our own mind very happily 

 conceived, so as to favour the grouping of those beings which have between them the 

 largest number of common characters, than with any of those which are after them the 

 most nearly related. That is a natural system, and consequently rational one ; the genera 

 represent equal degrees, and of comparable organization. That it is while, considering 

 them in this manner, that in our actual researches they acquire the most interest. The 

 fundamental basis of natural history, reposing on the exact and profound knowledge of 

 the species, being that which emanates directly from the hands of the Creator, while the 

 art of grouping those which we have recognised is human." Darwin considers the term 

 species, on the contrary, as one arbitrarily given, for the sake of convenience, to a set of 

 individuals closely resembling each other ; and that it does not effectually differ from the 

 term variety, which is given to its less distinct and more fluctuating forms. That the 

 term variety, again, in comparison with mere differential differences, is also applied 

 arbitrarily and for convenience sake ; that no one can draw any clear distinction between 

 individual differences and slight varieties, or between more plainly marked varieties and 

 sub-species and species. 



strenuous efforts have not shown the existence of more than about 80. Mr. Kelly, whose knowledge of 

 Irish geology is equal to that of any other man, and who has visited almost every Irish fossiliferous 

 locality, expresses himself averse to my rejecting so many Devonian and Silurian species said to have been 

 found in his carboniferous strata and localities, but I may again, without hesitation, assert that the larger 

 number, at any rate, are due to incorrect identification, for the examination of many of the original 

 specimens in Sir Richard Griffiths' and other collections have convinced Prof, de Koninck, Mr. Salter, and 

 myself of this important fact. 



Mr. Kelly has, however, informed me by letter that a large portion of the doubtful fossils were got in 

 localities of the calciferous slate, a band which lies under the limestone ; that out of about 70 not proved 

 to me, because I have not seen specimens, 22 were obtained at Lisnapaste and Donegal ; that in these 

 localities there is a great variety, and that they occur in black soft shale, as soft and as easily decomposed 

 by exposure to the atmosphere as any that occurs in the coal-measures : that a lump of this black shale 

 exposed to sun and rain for one summer, would slake or fall to pieces : and he therefore supposes that by 

 far the larger number of Lisnapaste specimens that were originally in Sir R. Griffiths' collection were lost 

 by their removal to the Great Exhibition held in Dublin in 1852, as those tender shales would not bear the 

 agitation of carriage, and consequently mouldered away into very small fragments. That there are six or 

 eight other localities in the calciferous slate in which similar shales occur with fossils, and that he finds, 

 upon looking over his lists, that most of the Devonian species I object to were obtained in those localities. 

 Along with Lisnapaste there is Larganmore, Bruckless, Kildress (the red shales near Cookstown in the old 

 red series), Bundoran, Malahide, Curragh, &c. 



