ZONE OF MISSOURI FLORA IN BRITISK SERIES. 297 



to bind our flora to the Middle Coal Measures. But the characteristic floras 

 of these British groups are more conspicuously marked by the important 

 additions which enrich the variety of plant life as we pass upward than b}" 

 the disappearance of the older forms, though the latter feature is clearly 

 indicated and of great service. The development of the Pecopteroid flora 

 appears to be confined in Great Britain almost exclusively to the Upper 

 Coal Measures. And it is largely to the proportion of identical or related 

 species of Pecopteris and the intimately connected Aplilebice that the approxi- 

 mate equality of the percentages in this table is due. It must, however, be 

 borne in mind that the Middle Coal Measures of England contain a number 

 of more recent species, such as Pecopteris polymorpha Brongn., P. Miltoni 

 Artis, and P. pteroides Brongn., which are of generally younger rank than 

 the flora from Missouri. Among the extensive material from the Radstock 

 coal field in the Lacoe collection the higher forms are in abundance, not- 

 withstanding the presence of very many species in common with those 

 from the trans-Mississippian region. On the other hand, the younger types, 

 such as Pecopteris Jenneyi, P. CanclolUana, P. hemiteUoicles% and P. cf. arho- 

 rescens, are very rare in our flora. 



In view of the foregoing considerations it appears very evident that 

 the flora of Henry County is not older than that of the Middle Coal Meas- 

 ures of Great Britain. The presence in our flora, not onlj- of an equal 

 number of species, but also of a considerable number of younger types 

 identical with or closel)^ related to those of the Upper Coal Measures justi- 

 fies the belief that our flora is not much 3-ounger than the Upper Coal 

 Measures, and that, considering its almost equally close relation to that of 

 the Middle Coal Measures, it may safely be considered as intermediate 

 between the two, or as occupying approximately the position of the "tran- 

 sition beds,"^ with a very intimate connection with the flora of the Upper 

 Coal Measures, The plants of these beds are very imperfectly known, but 

 from the common facies of their flora as yet revealed I am at present dis- 

 posed to regard these terranes as not younger than the lower coals of 

 Henry County. The flora of the latter may even correspond in part to 

 that of the basal portion of the Upper Coal Measures in the British coal 

 fields. 



'The "New Rock'' and the "Vohster Series" of the Bristol and Somerset coal held and the 

 "Lower Pennant" of the South Wales coal field. 



