DESCltlPTIOX OF THE SPECIES. 287 



ing but always small depth ; no midrib seen ; the base and summit of the 

 leaves not found ; the nerves very slender and seen with ditHculty, the}' are 

 several in number, of about the same strength, and apjjear to diverge from 

 the base of the leaf with a tlexuous coiu'se; they unite to form a series 

 of large, elongate, subrhombic meshes ; slender branches appear to enter 

 each tooth. 



Localities : Belt and Covington streets, Baltimore. 



This species is one of the abundant plants at tlie.se localities. The leaf- 

 fragment, PL CLXXII, Fig. 4, is very imperfect, since the margins have all 

 been removed. Tlie shape of these leaves is more like that of some of the 

 species of Protea, while the nervation resembles that of some of the species 

 of Pcrsoonia. 



ROGERSIA, gen. nov. 



Leaves long, narrow, and willow-like, wedge-shaped at base, acute, with 

 a very strong midnerve and very slender primary nerves ; these go off very 

 obliquely and diverge very slowly from the midrib, running for a long dis- 

 tance nearly parallel with the margins of the leaves; they anastomose with 

 branches sent off from other nerves of like grade higher up to form very 

 long, irregularly shaped, and lax meshes; ultimate reticulation oblong, sub- 

 rhombic, of quite uniform dimensions This genus is named for Prof W. 

 B. Rogers, who first called attention to the plants of the Potomac formation 

 and studied its geology. 



RoGERSIA LONGIFOLIA, sp. nov. 

 Plate t'XXXIX, Fig. 6; Pluto CXLIV. Pig. •>; Phite CL, Pig. 1 ; Plato CLIX, Figs. I, a. 



Leaves narrowly elliptical, gradually narrowed to the base and apex, 

 with wedge-shaped base, acute, very long in proportion to width ; midrib 

 comi)aratively verv stout; primary nerves very slender, going off very 

 ()l)li(pielv, [)roceeding u[)\var(ls for some distance nearly parallel with the 

 margin, but gradually approaching it ; primary nerves sending oH' very 

 obliquely secondary nerves, which anastomose with their neighbors to 

 form elongate, subrhombic, and irregular meshes, which have their maximum 

 dimensions turned upwards and slightlv outwards; primary meshes tilled 



