14G THE POTOMAC OR YOUNGER MESOZOIC FLORA. 



Locality: Red clay ball in the banks of Dutch Gap Canal; rare. 



This is a well marked species. Its rarity may be only apparent. The 

 plants found in tlie red clay ball form a peculiar assemblage, a number of 

 them, as in tliis case, being found nowhere else. The amount of material 

 in this ball was small, and owing to this, we can not say whether or not 

 the plants found in it were actually rare in the stratun represented by this 

 ball, and from which it was torn. It would seem that this ball belonged to 

 a fossiliferous layer, not now to be seen in place in the exposures about 

 Dutch Gap. No doubt many originally rich fossiliferous layers have been 

 destroyed in the local erosions to which the formation was from time to 

 time in the course of its deposition subjected. 



The plant is possibly composite in nature, and not a sharply differen- 

 tiated Osinunda, but as it contains more of the features of this genus than 

 any other, I have placed it there. The sori are very small, being fine dots. 

 The exact details of their structure could not be made out. 



OSMUNDA DiCKSONIOIDES, Sp. nOV. 



Plate XLI, Fig. 5 ; Plate LVIII, Fig. 9; Plate LIX, Figs. 1, 4, 8, 9, 11; Plate LX, Figs, a, 4, 5, 9; 



Plate LXI, Figs. 1, 2. 



Sterile frond large, arborescent, tripinnate ; rachises stout, especially 

 the principal ones; ultimate pinnai subopposite to alternate, closely placed, 

 linear-lanceolate, acute, ending with pinnules reduced to united teeth and 

 passing towards the summits of the compound pinnse into pinnules; pin- 

 nules or reduced pinnae alternate, closely placed, oblong to ovate, passing 

 above towards the tips of the compound and ultimate pinnse through oblong 

 or ovate lobed or toothed pinnules into entire ones, and finally into united 

 teeth, ovate-acute in form. The lower pinnules or reduced pinnse are much 

 narrowed at base, cut more or less deeply into ovate, elliptical, subquad- 

 rate, acute lobes and teeth, the lobes, especially the basal ones, being- often 

 toothed ; the nerves in each lobe composed of a midnerve sending off 

 obliquely and alternately branches either forked or simple; reduced in the 

 teeth of the upper pinnules and of the terminal portions of the lower ones 

 to forked or simple lateral nerves in each lobe or tooth ; the fertile frond 

 distinct from the sterile one ; the pinnules of the former much reduced in 



