570 MR ROBERT KIDSTON ON 



Pecopteris Serlii, Bgt. 



Haivlea abbreviata, L. & H. (not Brongt.) * 



Cordaites, sp. 



Lepidodendron, cf. Haidingeri, Ett. 



From Nevill's Colliery, near Llanelly, he recorded the following plants : — 



Catamites, cf. ramosus, Artis. 

 ,, cf. gigas, Brongt. 

 Annularia sphenophylloides, Zenker, sp. 

 Asterophyllites equisetiformis, Schl., sp. 

 Neuropteris, cf. Loshii, Bgt., with 

 Cyclopteris (separated pinnules). 

 Lepidodendron (showing Ulodendroid condition). 

 Sigillaria (?), cf. denudata, Gopp. 



In regard to the plant he identifies in great doubt as Sigillaria (?), cl. denudata, 

 Gopp, from the description Dr Stur gives of his specimen, there cannot be much doubt 

 that his plant is Sigillaria camptotamia, Wood, sp. 



From the occurrence of Pecopteris Serlii, Brongt., in the collection, Dr Stur refers the 

 rocks from which the specimens were derived to the Upper Coal Measures, correlating 

 them with the Rossitz beds near Brlinn, Moravia. I am, however, doubtful if the latter 

 correlation is correct. 



On the evidence of the occurrence of Alethopteris [Pecopteris) Serlii, Dr Stur also 

 refers the Bristol Coal Field, the Forest of Dean Coal Field, and the Forest of Wyre to 

 the Upper Coal Measures. In regard to the Bristol Coal Field, the two uppermost series 

 are referable to the Upper Coal Measures, though its lower beds cannot be referred to 

 so high a horizon. The Forest of Dean is true Upper Coal Measures, but the Forest 

 of Wyre is Middle Coal Measures. All these localities he regards as the representatives 

 of the Rossitz beds, but this is certainly incorrect in regard to the Forest of Wyre. 

 Although Alethopteris Serlii is a most characteristic fern of the Upper Coal Measures, 

 where it occurs in great profusion, it is not restricted to the Upper Coal Measures, but 

 first appears in the Middle Coal Measures, where, however, it is extremely rare. It is 

 quite unsafe, in almost all cases, to fix a horizon on the occurrence of a single species, 

 and this want of due precaution has done much to bring the evidence derived from 

 palaeontology in the correlation of strata, into disrepute. Equally important is it to 

 note the frequency in occurrence of a species, a point almost as important in determining 

 horizons as the mere occurrence of any given individual. Alethopteris lonchitica is 

 quite as characteristic of the Lower and Middle Coal Measures as Alethopteris Serlii 

 is of the Upper Coal Measures, but Alethopteris lonchitica has also been found, though 

 very rarely, in the Upper Coal Measures of Somerset where A. Serlii is so extremely 



* According to Stur. 



