A REVISION OF SEVERAL GENERA OF GYMNOSPERMOUS 

 PLANTS FROM THE POTOMAC GROUP IN MARYLAND 

 AND VIRGINIA. 



By Edward W. Berry, 



Of the Johns Hopkins University, Baltimore. 



The present paper is the third of a series of revisions of the more 

 important genera of fossil plants from the Potomac group in Mary- 

 land and Virginia. The 'first dealt with the genus Nageiopsis and 

 formed No. 1738 of Volume 38 ' of the Proceedings. The second 

 treated the genera Acrostichopteris, Taeniopteris, Nilsonia, and Sap- 

 indopsis and constituted No. 1769 of the same Volume 38. 2 



The present contribution is devoted to a consideration of the genera 

 Sphenolepis, Arthrotaxopsis, Cephalotaxopsis, Widdringtonites , Brachy- 

 plvijllum, Sequoia, Abietites, and Pinus. These are all gymnosper- 

 mous genera, some of which are of disputed botanical affinity. The 

 majority offer exceptional difficulties to their correct interpretation 

 by reason of the convergence in foliar characters of the Mesozoic 

 Coniferales. This is more marked than in the existing species 

 because of the greater number of species in the Mesozoic, a period 

 which has more than once been termed the "Era of Gymnosperms." 



The genera Arthrotaxopsis and Cephalotaxopsis were originally 

 described from the Potomac group. All of the other genera, how- 

 ever, are well known and for the most part widespread Mesozoic 

 types, two, Sequoia and Pinus, surviving to the present time. 



In the previous treatment of these types in the area under dis- 

 cussion there existed the utmost confusion and it has been necessary 

 to check each cited occurrence by referring back to the original 

 material in the U. S. National Museum collections. This has 

 resulted in a most intricate splitting and combining of the named 

 forms or parts of the named forms as they occurred in the literature, 

 some idea of the extent and labor of which can be imagined from the 

 following synonymy. 



Forty-three species and three varieties which were formerly recog- 

 nized are here replaced by 18 species. Instead of 9 species and 1 variety 

 of Sequoia four are retained; 6 species and 1 variety of Sphenolepidium 



» Pp. 185-195. 2 Pp. 625-644. 



Proceedings U. S. National Museum, Vol. 40— No. 1 821 . 

 80796°— Proc.N.M.vol.40— 11 19 289 



