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DR. STANLEY SMITH ON AVLINA HOTIFOHMIS, [vol. lxxii, 



Plate XXIV. 



Orionastrsea and Lithostrotion. 



All forms are from the upper part of the Dibunophyllum Zone. 



Fig. 1. Orionastrsea phillipsi (McCoy). Transverse section. X 2. Upper 

 Grey Limestone. Hafod-y-Calch, Corwen. British Museum 

 (Natural History), R 4510 (G. H. Morton Collection). A typical 

 section of the species. (See p. 299.) 



2. Orionastrsea phillipsi (McCoy). Distal surface. Natural size. 



Hafod-y-Calch, Corwen. British Museum (Natural History), 

 R 4575 (G. H. Morton Collection). This specimen illustrates the 

 variability of distal characters. (See p. 298.) 



3. Orionastrsea ensifer (Edwards & Haime). Neotype. Transverse 



section. X 2. Clifton, Bristol. British Museum (Natural 

 History), R 17084 (S. G. Perceval Collection). (See p. 302.) 



4. Orionastrsea ensifer (Edwards & Haime). Longitudinal section. 



X 2. South- West of England. British Museum (Natural 

 History), R 17087 (S. G. Perceval Collection). 



This also illustrates a characteristic longitudinal section of 

 O. phillipsi, (On account of their tortuous mode of growth, great 

 difficrdty has been encountered in obtaining an accurate medial 

 section through the corallites of the corals for more than a short 

 distance, as seen in the present case.) 



5. Orionastrsea ensifer (Edwards & Haime). Distal surface of the 



neotype (R 17084). Natural size. (See p. 302.) 



6. Lithostrotion basaltiforme auctt. Distal surface. Clifton, Bristol. 



Natural size. British Museum (Natural History), R 4547 (G. H. 

 M«rton Collection). (See p. 302.) 



The figure is here included, in order to illustrate the difference 

 "between Lithostrotion, with its well-developed epitheca separating 

 the individual calices, and Orionastrsea ensifer, in which the calices 

 merely meet in a sharp ridge. 



DlSCUSSTON. 



Prof. E. J. Garwood congratulated the Author on a further 

 contribution to the good work that he had already done in revising 

 different groups of Lower Carboniferous corals. He quite agreed 

 with him that the form, generally known as ' Phillipsastrcea' 

 radiata, which occurs in the Botany Beds in Yorkshire and also in 

 the Fell Top Limestone of Northumberland, was a distinct form 

 apparently limited to a high horizon in the Yorkshire beds, and he 

 had himself used it as a zonal index for this horizon. He pointed 

 out that at Botany the beds still contain abundant examples of 

 Dibunophyllids and other well-known marine Lower Carboniferous 

 forms, although they occur some 200 feet above the base of the 

 Millstone Grit Series uf the Geological Survey maps. It was 

 obvious, therefore, that, however useful it might be for economic 

 purposes to represent the arenaceous occurrences by a special colour, 

 this sandy episode entered in different districts at different periods, 

 and could not be used as a definite stratigraphical horizon dividing 

 the Lower from the Upper Carboniferous rocks. 



Prof. T. F. Siblt Avished to compliment the Author on the com- 

 pletion of yet another excellent pakeontological investigation, and 



