62 PP. REPORT OF PROGRESS. FONTAINE & WHITE. 



There is a tendency to pass into the form of Callipteridium, 

 even in cases where the departure is not sufficient to separ- 

 ate the jjlant from Pecopteris. The pinnae of the last order 

 often assume an elongate, linear form, and the pinnules, a 

 falcate shape not usually seen in the Pecopterids of lower 

 horizons. We also find that the lowest pinnule, on the 

 lower side of the ultimate pinnge, is often heteromorphous, 

 and inserted partly on the rachis of superior order. The 

 forms occurring in older strata which do pass up into the 

 upper beds are generally considerably changed, so as to 

 present a different facies, though they retain the leading 

 features on which their specific value depends. In the 

 case of some the change is so great that we may have erred 

 on the side of conservatism in identifying them with species 

 already described. 



The plants of this genus which, being found in older 

 strata, also occur at the higher horizons are those which 

 immediately follow. 



Pecopteris arborescens, (Schloth.) Brongt. 



The representatives of this species are among the most 

 abundant of the jjlants, occurring in the upper horizons. 

 Among the many specimens seen, we find none that agree 

 entirely with the typical form of the plant as seen in the 

 lower horizons of the Carboniferous Strata. 



Nearly all tlie forms seen are more closely allied to the 

 Permian plant which Groeppert has described under the 

 name Cyatlieites Schlotheimii. Many specimens are much 

 more delicate and finely cut than Groeppert' s plant. The 

 characters of this form are so constant and distinct that it 

 may well be questioned whether it should not remain a dis- 

 tinct species. We find this plant in every portion of the 

 upper beds where fossils are found, as at Carmichaels in 

 Pennsylvania, and at Cassville, West Union, Bellton, &c. in 

 West Virginia, both associated with the Waynesburg Coal 

 and at higher levels. Along North Ten Mile Creek in 

 Washington Co. Penn. it is very abundant at the horizon 

 of the Washington coal. 



