104 THE POTOMAC OR YOUNGER MESOZOIO FLORA. 



They extend from the base to the summit of tlie pinnules. The arrange- 

 ment of the sori indicates that the fructified pinnules in the lower pinnne 

 are toothed or lobed,*and that towards tlie summit of the compound pinnas 

 ^they graduate into lobes and teeth. 



Locality: Hill-side near Potomac Run; very abundant. 



The fructified forms are the common ones, sterile forms are very rare. 

 Numerous specimens, such as are depicted in PI. LIX, Fig. 12, and PI. 

 LX, Fig. 7, and smaller ones, may Ije found here, the pinnules being 

 reduced to imprints of the sori and principal nerves. The plant seems to 

 be a very well marked new species. 



POLYPODIUM, L. 



The genus Pohjpodium, if it exists in the Potomac flora, is not repre- 

 sented by many species. The imperfect preservation of the; specimens 

 does not permit the certain determination of the genus, but there are two 

 species which agree better with this genus than any other, and for this 

 reason I place them provisionally in it. 



POLYPODIUM FADYENIOIDE, Sp. UOV. 

 Plate XVI, Figs. 4, 5. 



Pinnules narrow and linear, obtuse; fragments of the fertile ones 

 alone were seen; leaf-substance very thick and leather}-; sori ver}- large, 

 globose in shape, placed on the ends of strong simple lateral nerves, 

 which are at their summits expanded into club-shaped receptacles arranged 

 in a row on each side of the midnerve of the pinnules, a little within the 

 margin, and extending nearly from the midnerve to the margin. 



Locality: Road-side near Potomac Run; very rare. 



The pinnules of this plant seem to have been narrow and long, very 

 thick and leathery. The club-shaped sununits of the nerves which sup- 

 ported the sori appear, when the upper surface of the pinnules is presented 

 upwards, showing through the leaf-substance as elliptical elevations, look- 

 ing like sori, as shown in Fig. 5. Figure 4 represents, slightly enlarged, a 

 fi-agment of a much longer pinnule with the lower side uppermost, showing 

 tlie character of the very large soi-i. A granulation is seen with the help 



