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XXVI. — The Ordovician and Silurian Brachiopoda of the Girvan District. By 

 F. R. C. Reed, M.A., Sc.D., F.G.S. Communicated by Dr Horne, F.R.S. 

 (With Twenty-four Plates.) 



(MS. received November 2, 1914. Read February 15, 1915. Issued separately February 2, 1917.) 



Introductory Remarks. 



The principal descriptions and figures of the Ordovician and Silurian brachiopods 

 of the Girvan district are found in Davidson's Monograph on the British Fossil 

 Brachiopoda, completed about thirty years ago, and issued by the Palseontographical 

 Society. The third volume of this work (published 1866-1870), and the Supplement 

 to the fifth volume (published 1882-1883), dealing with species from Ordovician and 

 Silurian beds, contain descriptions of many Girvan forms, but not apart from those 

 occurring in other British localities. No independent and comprehensive treatise 

 on this group as represented in the Girvan area has been published, though many 

 short papers have dealt with a few species or portions of the fauna. Especially 

 noteworthy are the papers and works by M'Coy and Salter, mentioned in the 

 list at the end of this memoir. , 



The attempt to refer fossils to well-known and previously established species in 

 spite of minor morphological differences was a common custom in the past, and was 

 partly due to the imperfect correlation of stratigraphical horizons. But the general 

 disinclination to multiply specific names was the main influence at work, particularly 

 when the variability of all organisms was recognised. The result of this attitude 

 was that specific conceptions became too comprehensive and indefinite, and it is 

 only of late years that small differences of character have been adequately admitted 

 to be important from the zonal, distributional, and zoological points of view. 



The diagnoses of species given by earlier investigators suffered from looseness, 

 mdefiniteness, or brevity ; but some modern palaeontologists are not wholly free from 

 the same reproach, and even at the risk of inserting superfluous detail it has 

 seemed best to the present writer to err on the side of fulness in describing any 

 new species. 



All previous work on the Girvan brachiopods has been hindered by the paucity 

 or poor preservation of the material available, and under such conditions the in- 

 correct identification of some forms was unavoidable. Such difficulties have been 

 removed to some extent by the larger collections and better specimens which are 

 now open to examination, but in many cases we have still to confess imperfect 

 knowledge owing to the fragmentary condition of the fossils. In nearly every case 

 Davidson's figures are restorations of the actual specimens, and unfortunately they 

 are frequently inaccurate and misleading. 



TRANS. ROY. SOC. EDIN., VOL. LI, PART IV (NO. 26). 116 



