BRITISH ORDOVICIAN AND SILURIAN 

 BELLEROPHONTACEA. 



INTRODUCTORY REMARKS. 



Theee has been no recent detailed study of the species of tlie Bellerophontacea 

 occurring in the British Ordovician and Sikirian rocks, and the existing nomen- 

 clature, particularly of the genera, is in a state of considerable confusion. 



The poorness of most of the material has always proved a serious obstacle to 

 the satisfactory determination of British species, and tbis difficulty has only been 

 partly removed by the author's examination of a large number of specimens. The 

 types of Sowerby's species have been re-examined, and a revised and fuller descrip- 

 tion of them has been drawn up with the additional aid of further examples 

 from the original localities, whenever such has been possible. 



The material from Girvan which has been submitted to me by Mrs. Gray, is 

 occasionally in a good state of preservation and comprises many new forms. 

 Mr. Turnbull's collection from Haverfordwest has also proved of considerable 

 interest. But apart from Mrs. Gray's collection the majority of the fossils which 

 have been studied are in the Sedgwick Museum, Cambridge, the Museum of 

 Practical Geology, Jermyn Street, London, and the British Museum (Nat. Hist.), 

 South Kensington, and my thanks are due to the authorities, who have given me 

 every assistance in studying the specimens. 



CLASSIFICATION. 



Our knowledge of the structure of this interesting group of Mollusca as 

 represented in Ordovician and Silurian beds, has been much advanced of late years 

 by the labours of Koken,^ Lindstrom,^ Ulrich and Scofield,^ and Pernei%* while 



' Kokeu, 'Neues Jahrb. f. Miner.,' suppl. vol. vi (1889), pp. 375—395; 'Die Leitf ossilien ' 

 (Leipzig, 1896), pp. 100, 392, 393; "Die Gastrop. Bait. Untersilurs." ('Bull. Acad. Imp. Sci. St. 

 Petersburg' [v], vol. vii, no. 2, 1897), pp. 115—143; and ' Neues Jahrb. f. Miner.,' 1898, vol. i, 

 pp. 3—11. 



2 Lindstrom, "Silur. Grastrop. Pterop. Gotland" ('Kongl. Svensk. Vet.-Akad. Handl.,' vol. x, 

 no. 6, 1884), pp. 69—88. 



^ Ulrich and Scofield, " Lower Silur. Gastrop. Minnesota " (' Final Kep. Geol. Nat. Hist. Surv. 

 Minnesota,' vol. iii, pt. ii, 1897), pp. 844—929. 



4 Perner, ' Sjst. Silur, Bolicme,' vol. iv, Gastrop. I (1903). pp. 54—162. 



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