128 THE POTOJIAO OR YOUNGER xMESOZOIC FLORA. 



ultimate piunte becoming- entire and narrowly elliptical. In tliis j^ortion of 

 the frond there is a distinct midnerve in each pinnule, which at its summit 

 splits into branches, while it sends off alternately and ol)liquely on each 

 side lateral nerves into the lobes. These in the basal lobes have a mid- 

 nerve which sends otf alternately on each side simple nerves, and in those 

 up higher they fork once or twice ; pinnules of the middle portion of the 

 frond and compound pinnae (see PI. XLII, Fig. 2) are remote, linear, acute, 

 and decurrent to form a wing, cut into acute short teeth; midnerve and 

 lateral nerves of these rather .slender but distinct; lateral nerves of each 

 tooth forking deeply, one branch ending in the tip of the teeth; pinnules of 

 the upper part of the frond and compound pinuie (see PI. XLII, Figs. 1, 

 4) reduced to narrowly oblong lobes and teeth. The ultimate pinnaj also, 

 in passing- to the upper portions or tips of the compound pinnaa, pass into 

 lobed and toothed pinnules similar to those down lower. The compound 

 pinnae most probably end abruptly Avith a terminal pinnide like those 

 lower down. (See PI. XLIII, Fig. 1.) 



Localities: Fredericksburg ; road-side near Potomac Run ; ratlier 

 abundant at the former place, rare at the latter. 



The variability of this splendid plant causes it in one or another of 

 its forms to approach several that are described imder other names. It 

 belongs to the Spheiiopteris Ilanfelli type of Tlii/rsopteris, but the thick 

 leaf-substauce, remoteness of the pinnae and pinnules, the strong wing, 

 and the once forking lateral nerves distinguish it. In PI. XLIII, Fig. 1, 

 the tip of a compound pinna is shown, and it has abruptly terminating it 

 a pinnule similar to those lower down. It is a good deal like T. insignis, 

 var. angustipennis, as shown in PI. XLIII, Fig. 3, but this latter does not 

 have the rachises winged. Among described fossils we find Aspidium 

 Johnstriqri, Heer,^ something like the plant now in question. 



Thyesopteeis iNSiGNis, var. angustipennis, sp. nov. 



Plate XLII, Fig. 3; Plate XLIII, Fig. 2. 



Frond bipinnate or tripinnate, arborescent ; rachises stout and promi- 

 nent ; leaf-substance thick and leathery ; ultimate pinnae alternate ; pinnules 



• Coiupaie Flor. Foss. .Ire, vol. 3, No. 2, PI. I, Figs. 6, 7. 



