

Vol. 67.] THE AVONIAN OF BUKKINGTON COMBE. 371 



This fauna agrees with that of D x at all other points of the South- 

 western Province, and is closely similar to that of the same level 

 in the North- Western Province near the top of the Great Scar Lime- 

 stone. It is, in fact, astonishing how close is the resemblance of 

 the South- Western and North-Western Provinces at this horizon. 



This division — the top of the Carboniferous Limestone in the 

 Bristol Area — is covered by Triassic rocks in the syncline between 

 Burrington and Wrington, but must be continuous with the fine 

 exposure of fossiliferous beds in the quarry overlooking W^rington. 

 The fauna of these beds is described in the ' Bristol Paper V Theso 

 beds maybe correlated with the top of the Great Scar in the North- 

 Western Province, where they are capped by the Yoredales, to which, 

 in the South- Western Province, there is no fossiliferous equivalent 

 except in Gower." 



IV. Palaeontology. (A. V.) 



(1) CORALS. 

 Michelinia. 



The two forms of greatest interest both occur in Z . 



Michelinia megastoma (Phill.), mut. Z 2 . 



This form has as yet no specific name, although its abundance in 

 many, and widely separated, districts at the same level makes it an 

 important zonal fossil. . 



The corallum is circular with a flattened base ; the calicinal 

 surface is gently convex. 



The corallites have large, approximately equal, apertures, and are 

 some ten in number. 



The walls of the calices are thick and almost vertical ; the calices 

 are deep, so that there is little room between floor and epitheca for 

 the development of vesicular tissue, and the internal structure is 

 almost entirely concealed by the growth of stereoplasm. 



The epitheca is concentrically wrinkled, without roots. 



This mutation is common in Z at Burrington, Stackpole Quay, 

 Malahide, etc. 



There can be little doubt that this mutation passes up into the 

 typical M. megastoma, a species that has its maximum in C-S, and 

 only differs from the Z mutation in greater size and in the propor- 

 tionately larger number of corallites. 



The megastoma beds of Bush (C-S) contain the typical M. mega- 

 stoma in abundance. 



At Burrington the place of M. megastoma is taken by M.grandis, 

 and the rule seems to be generally true that M. megastoma and 

 M. grandis are, to a considerable extent, mutually exclusive. 



L Q. J. G. S. vol. lxi (1905) p. 242. 



2 Abs. Proc. Geol. Soc. 1909-10, pp. 72-73. 



