358 ME. T. F. STBLY ON THE CARBONIFEROUS [May I906, 



area, than is the case with any other part of the sequence. Con- 

 sequently, very few points call for special mention. 



(a) The common occurrence of Athyris cf. eocpansa in the 6ty>- 



subzone of the Mendip sequence constitutes a noticeable 

 difference. 



(b) Distinctive features of the Lonsdalia-suhzoTie, in the Mendip 



area, as compared with the Bristol area, are : — 



(1) The great abundance of a well-defined member of the group of 



giganteid Producti, namely, Productus 0. 



(2) The great abundance of Productus concinnus, mut. D. 2 in the upper- 



most beds. 



The LonsdaUa-suhzone in the Mendips has not yielded so prolific 

 a coral-fauna as that found in D 2 of the Bristol area, but this is, 

 doubtless, due to the small number and limited extent of the 

 exposures. 



Horizon e. 1 



So far as I am aware, this horizon is not exposed in the Mendip 

 area. Consequently, we are for the present ignorant of an 

 important matter, namely, the exact position which this horizon 

 occupies with regard to the base of the ' Millstone Grit ' in the 

 Mendip sequence. 



Note on the Separation of the Syringothyris-Zone and the 

 Seminula-Zone in the Mendip Area. 



In the sequence typical of the Bristol area, the palaeontological 

 break in the middle of the Avonian renders the separation of the 

 Syringothyris- and Seminula -Zones an easy matter, for the upper- 

 most part of C consists of unproductive shales and dolomites, and, 

 when 1'ossiiiferous beds are again met with, they are found to contain 

 a typical Seminula-faxma,. In the Mendip area, however, where 

 the upper part of C and the lower part of S form a continuously- 

 fossiliferous sequence, and the change from a typical Syringothyris- 

 fauna to a typical Seminula-f&xmvL is gradual, the separation of the 

 two zones requires special definition. 



There is no well-defined horizon of faunal overlap between C and S 

 in the Mendip sequence. Giganteid Producti, including Productus 

 aff. Cora, mut. C and Pr. 6, occur commonly throughout the upper 

 part of C, and Seminula aff. Jicoides enters sparingly in the upper- 

 most beds. These facts do not, however, justify a separation of the 

 uppermost part of C (which contains Sy ringothyris aff. cuspidata, 

 mut. C, but no LitJiostrotion Martini), 2 as a definite horizon of overlap. 

 Again, the subzone S x contains a predominant Semimda-ia,uv.& 

 associated with certain survivors of the Syringothyris-fami'd, but 



1 See A. Vaughan. Quart. Journ. Geol. Soc. vol. lxi (1905) p. 262. 



2 Lithostrotion cf. irregulare occurs in the uppermost beds of C, but has not 

 been found in S x . 



