BRITISH SILURIAN BRACHIOPODA. 223 



I have followed, in this Supplement, the stratigraphical divisions of the Ayrshire 

 Silurian deposits so ably propounded by Prof. 0. Lapworth/ from which it will be 

 observed that the species from the Craighead beds are now placed in the " Llandeilo " 

 instead of the " Caradoc," to which they were supposed to belong at the time I was 

 publishing my ' Silurian Monograph.' I have also considered it desirable to give two 

 separate Tables in the first of which I include those species which have been obtained from 

 Ayrshire ; and in ihe second those that have been found in the seven other Scottish Silurian 

 Counties. I have done this because it was not possible, in the present state of our 

 information, to refer some of the species to their respective geological horizons with as 

 much minuteness as had been done for Ayrshire. It is also true that in the Explanations 

 of one or two Sheets of the Map of the Geological Survey of Scotland some species are 

 recorded, in particular from the Leadhill district, that are not included in my second 

 Table ; but I have considered it desirable to omit them, as the specimens on which the 

 determinations had been founded were lost or missing, and because I greatly doubted the 

 correctness of their identification. 



Some of our Scottish specimens and species will, however, still demand much further 

 study before they can be definitely admitted. This, however, can only be effected in 

 time by the discovery of more complete material ; and there certainly remains very 

 much to be worked out by future palasontologists, who, I feel certain, will not relax in 

 their endeavours to complete and extend what has been so far achieved. 



any. In 1838 Mr. C. Maclaren was more fortunate, as he found an Orthoceras there, but no Brachiopod, 

 and it was not until 1858 that the first Brachiopod was discovered by Prof. A. Geikie. 

 1 'Quarterly Journal of the Geol. Soc.,' vol. xxxviii, p. 537, &c. 1882. 



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