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XVIII. — The Lamellibranchs of the Silurian Rocks of Girvan. By Wheelton Hind, 

 M.D., B.S., F.R.C.S., F.G.8. Communicated by Dr J. Horne, F.R.S. (With 

 Five Plates.) 



(MS. received February 2, 1910. Bead March 16, 1908. Issued separately August 30, 1910.) 



Introduction. 



The task of examining and determining the fine series of lamellibranchs collected by 

 Mrs P. Gray in the Girvan district, from rocks of Llandeilo, Bala, and Llandovery age, 

 has been no light one. In the first place, the literature of the subject is very scattered, 

 and is chiefly to be found in the various reports of the Geological Surveys of the 

 different States of North America and Canada. The work of British palaeontologists is 

 to be found in the publications of the Geological Survey and in various periodicals, but 

 nothing systematic has been attempted before in this country, although Sowerby 

 described and figured, in an appendix to Murchison's Silurian System, all the known 

 species. Under these circumstances there has been the greatest difficulty in studying 

 original types, many of which are Swedish or North American. 



I have to acknowledge my obligations to Dr Teall, the Director of H.M. Geological 

 Survey, and the Palaeontologists, Dr Kitchin and Mr Allen, who have placed all 

 their type specimens at my service ; and to Mr H. Woods, of the Sedgwick Museum, 

 Cambridge, who has also lent me the species described by M'Coy in his British 

 Palwozoic Rocks and Fossils. But unfortunately these fossils were not of much assist- 

 ance, for I found that few of them were represented in the suite of specimens from 

 Girvan, and have therefore had to trust, in many cases, to the descriptions and figures 

 of American authors for the identification of the species. 



The number of specimens in Mrs Gray's collection which I could refer to no known 

 species is comparatively large ; hence I have been compelled to describe a number of 

 new specific forms, often, unfortunately, on single specimens. Again, owing to the 

 indifferent preservation, or to the fact that the hinge plates and internal structures 

 were not exposed, difficulty has arisen in deciding as to which of the many genera 

 erected by American authors it was advisable to refer certain species. Hence, in the 

 future, fresh material may necessitate some revision in the names of genera now 

 assigned. 



The lamellibranch fauna as a whole has a very strong generic affinity with the 

 fauna described by Hall from the Devonian rocks of North America.* A com- 

 paratively large number of genera extend from Ordovician to Devonian time, though, 

 from our present knowledge, it would seem that the sprcies of each genus were far 



* Geol. Survey New York, Pal., vol. v., pt. i., Lamellibranchiata, pt. i. and ii. 

 TRANS. ROY. SOC. EDIN., VOL. XLVII. PART III. (NO. 18). 71 



