1877.] 4:iO [Lesquereux. 



sitional, and affecting essentially the general features of periods. They give 

 to separate groups a peculiar character, which may serve to separate them. 

 In a lot of plants sent by Prof. Eug. Smith from Alabama, for example, 

 I found such a dissimilarity of typical forms from those of the coal meas- 

 ures of the north, and also such an affinity with those of the Arkansas sub- 

 carboniferous flora, that this relation forcibly referred both to the same 

 period. 



The distinctive characters of the groups of the Carboniferous can be only 

 briefly exposed now; but they are to be more positively fixed in the Flora by 

 separate tables indicating all the species of plants which have been recog 

 nized in each of them. This Avill prove an interesting representation of 

 the distribution of the vegetation of the coal, not merely by the number of 

 species, but especially as a kind of scale marking the progress in the modi- 

 fication either by disappearance of some types, or by their reproduction 

 under different characters. 



Tlie groups as recognized until now are the Catskiil, or old red ; the 

 Pseudo-carboniferous ; the Sub-carboniferous, or Vespertine, limited up- 

 wards by the millstone grit ; the Lower Carboniferous, up to the Pittsburgh 

 coal ; and the Upper Carboniferous, above it. 



A few species of small Lycopodiaceous plants of the genus Psilophyion 

 (Daws), appear first in the upper Silurian, and continue, by modifications of 

 size especially in the Devonian, where four species are recognized. I con- 

 sider this genus as representing the only Devonian type which does not 

 pass up into the Carboniferous. There may be some others, however, as 

 indicated bj' fossil wood : Dadoxijlon, Syringoxylon, Prototaxites, etc. But 

 the anatomy of the fossil wood of the whole Carboniferous is not yet ad- 

 vanced enough to allow conclusions on the characters of the vegetation 

 represented by fossil trunks. Prof Dawson is still pursuing with an in- 

 dustrious energy his researches on this difficult subject, which, to my re- 

 gret, has remained inaccessible to me for want of materials. For except 

 the fossil wood of the Black Devonian shale of Ohio, no specimen of 

 silicified vegetable organism has been discovered in coal measures of the 

 United States, except the numerous stems of fern trees of Southern Ohio. 

 These might give materials enough f(jr the work and studious applica- 

 tion of a wliole life. 



The more notable characteristic type of the Catskiil group is that of the 

 ferns described first under the generic name of Ifceggerathia, and more re- 

 cently of Pakeopteris and Archceopfei-is. The species are represented by 

 large fronds ; those of the older type with simple leafiets more or less en- 

 larged upwards from a narrowly cuneate, somewhat decurring base, whose 

 veins are straight and diverging, fan-like, merely by sub-divisions. The 

 forms of the leaflets are very variable ; some appear nearly linear and 

 merely thinly lined with parallel veins. These, however, pass to the genus 

 Cordaites, which is present in the whole flora of the coal measures. Tlie 

 modifications of Psilophytum are possibly represented in the Catskiil by a 

 few species of Lepidodendron. Catamites, Annularia and Asterophi/l- 



PROC. AMER. PHILOS. SOC. XVI. 99. 2z 



