130 THE POTOMAC OE YOUNGER MESOZOIC FLORA. 



ThYRSOPTEKIS CRASSINEEVIS, Sp. IIOV. 

 Plate XLI, Figs. 1-3. 



Frond bipinnate or tripinnate ; rachises all slender ; ultimate pinnpe 

 opposite or subopposite, short, subacute ; penultimate pinnse very long ; 

 upper basal pinnule of the ultimate pinnaB heteromorphous, much larger 

 than the others, cut more or less deeply into three obtuse lobes or teeth ; 

 pinnules mostly elliptical or subrhombic, lower ones separate to the base, 

 upper ones more and more united and passing into ovate lobes ; leaf- 

 substance thick ; nerves very strong, standing out like threads ; midnerve 

 of the pinnules splitting up into branches at the summit, sending off alter- 

 nately on each side latei'al nerves which branch once or twice, and in the 

 lobes of the heteromorphous pinnule sending off a flabellately diverging 

 nerve-bundle, the branches of which mostly fork near their ends. 



Locality : Fredericksburg ; rather rare. 



This belongs to the S2)]icnopteris type of Thyrsopteris, and resembles 

 in some respects several of that type, but. it is distinguished by its strong 

 nerves and heteromorphous upper basal pinnule. 



Thyksopteris decurrens, sp. nov. 



Plate XLIII, Fig. 7 ; Plate XLVI, Figs. 2, 4 ; Plate XLIX, Figs. 5-7. 



Frond tripinnate, arborescent, of large size!; principal rachis some- 

 what flexuous ; rachises of all orders winged ; pinnules decurrent, rather 

 remote, varying in shape according to position and consequent lobing 

 from oblong to linear-acute, diminishing much in size and depth of lobing 

 in ascending towards the summits of the compound pinna-, much narrowed 

 at base and going off" obliquel}' ; the lower ])innules deeply and obliquely 

 cut into narrow, oblong, obtuse lobes, upper ones narrowly oblong to 

 linear, with acute, elliptical, shallow teeth ; nerves in each lobe or tooth 

 distinct, in those of the lower parts of the pinnte deeply forked, in those 

 of the upper parts simple, all very oblique and approximately parallel. 



Localities : Red clay ball in banks of Dutch Gap Canal ; Fredericks- 

 burg; 72d mile-post, near Brooke; hill-side near Potomac Run; fishing- 

 hut above Dutch Gap Canal ; ii; all places rather rare. 



