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IX. — Lower Palaeozoic Hyolithidae from Girvan. By F. R. Oowper Reed, M.A., 

 F.G.S. Communicated by Dr Horne, F.R.S. (With Three Plates.) 



(MS. received March 5, 1909. Read June 7, 1909. Issued separately October 13, 1909.) 



Introduction. 



The extensive series of specimens of members of the Hyoliihidce which Mrs 

 Elizabeth Gray has collected from the Ordovician and Silurian beds of the Girvan 

 district, and submitted to me for investigation, forms the basis of the following memoir. 



Through the kindness of Dr John Horne and Professor J. W. Gregory, special 

 facilities have been afforded me of examining the other Scotch examples in the 

 Geological Survey Collection, Edinburgh, and the Museum of Glasgow University. 

 My thanks are also due to Dr F. L. Kitchin for the opportunity of studying the 

 specimens in the Jermyn Street Museum. 



The collections in the Sedgwick Museum, Cambridge, from various localities and 

 many Lower Pala30zoic horizons in Great Britain and Ireland, have enabled me to 

 compare the Girvan species with previously described and typical forms. The 

 specimens in the same museum from Bohemia, named by Barrande himself, have 

 proved of much value. Examples in the British Museum have also been consulted. 



The classification of the Hyolithidce drawn up by Holm is here followed, the 

 genus Hyolithes being divided into two principal subgenera, Hyolithes sens. str. 

 and Orthotheca, but Novak's Ceratotheca is retained as a third independent group of 

 generic rank for two doubtful species. The genus Pterotheca is also included in 

 the same family, but the reasons for doubting the accuracy of this customary 

 position are mentioned and briefly discussed. 



Genus Hyolithes, Eichwald, 1840. 



Subgenus Hyolithes, Eichwald -Holm, 1893. 



Hyolithes ardmillanensis, sp. nov. (PI. I. figs. 1-6.) 



Shell straight, short, broad, rapidly tapering at about 1 in 2|-, dorso-ventrally 

 compressed. Ventral face moderately convex, rounded or slightly subangular Dorsal 

 face flat. Mouth oblique, with strongly arched dorsal lip. Lateral angles sharp, 

 acute. Ventral face ornamented with 18-20 strong, rounded, straight longitudinal 

 raised lines, of equal or subequal size, and separated by wider interspaces. Dorsal 

 face, with fine concentric arched striae and traces of longitudinal folds, and occasionally 

 with shallow submarginal grooves visible in the cast. 



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