DESCRIPTION 01'^ THE SPECIES. 145 



lobes; lateral nerves of the [)iiniules few and remote, going pinnately on 

 each side of the niiihib into the lobes, and forking once or twice, all 

 strong. 



Locality : Hill-side near Potomac Rnn ; rare. 



This small plant reminds one of Thyrsopteris squanvsa, bnt appears to 

 be a well-marked distinct species, not nearly allied to any described fossil. 



Undetekmined Fern in ciecinate veknation. sp. ? 



Plate LIX, Ki},'. 5. 



Small, circinate fern fronds, similar to the form depicted in Fig. 5, are 

 quite common in the shale on the hill-side near Potomac Run. They 

 occur mostly in the form of small fragments. This locality is noteworthy 

 for the great number of specimens of a comparatively small number of 

 species of ferns that it atlbrds. It is eminently a fern locality, being the 

 only place where the specimens of that family surpass in numbers all 

 others put together. 



OSMUNDA, L. 



The genus Osmimda is not represented in the Potomac by many spe- 

 cies, but the number of individuals, of at least one of the species, is con- 

 siderable. 



OSMUNDA SPHENOPTEROIDES, sp. nOV. 

 Plate XXV, Fig. 13. 



Frond most probably bipinnatifid, spreading; rachises slender; sterile 

 and fertile pinnules on the same pinna ; lower pinnules of the ultimate 

 pinnae fertile, the upper ones sterile, occasionally some of the basal lobes 

 of the upper pinnules fructified ; pinnules alternate, remote, especially the 

 fertile ones ; fertile pinnules uuich reduced in size, oblong in form, with 

 bluntly rounded lobes, which are covered with sori ; sterile pinnules short, 

 cut more or less deeply into oblong, elliptical, subacute lobes, obliquely 

 placed, narrowed at base to a sort of petiole ; nei'ves fine, but distinct, 

 branching flabellately in eacli lobe or tooth, departing from a more or less 

 pi'onounced midnerve, the branches sometimes forked, but more commonly 

 simple. 



MON XV 10 • 



