140 THE POTOMAC OE YOUNGER MESOZOIC FLORA. 



lower ones cut obliquely into oblong or elliptical lobes or teeth, basal ones 

 sometimes blunt-lobecl, greatly narrowed at base, all minute ; leaf-substance 

 tliin ; nerves in the lobes or teeth slender but distinct, composed in the 

 pinnules of a midnerve with obliquely placed, alternate forking or simple 

 branches on each side, and in the lobes and teeth of lateral nerves, which 

 fork once or twice and go off very obliquely. 



Localities : Fredericksburg ; entrance to Trent's Reach ; White House 

 Bluff; fishing-hut above Dutch Gap Canal ; rare. 



This elegant little plant is one of the more widely diffused ferns. It 

 is noteworthy for the minuteness of the pinnules and lobes. It seems to 

 be a well-marked new species. 



Thyrsopteris microloba, sp. nov. 



Plate LVII, Fig. 4. 



Frond arborescent, tripinnate ; principal rachis proportionally very 

 stout, rigid, and prominent; penultimate pinnre alternate, closely placed, 

 much narrowed at the base, decurrent; lower pinnules of the ultimate 

 pinnjE elliptical, narrowed at base, slightly and obtusely toothed, minute, 

 the upper basal pinnule larger than the rest and more deeply toothed ; 

 pinnules on the upper side generally larger than those on the lower, and 

 showing a toothing up higher towards the tips of the ultimate pinna? ; 

 pinnules towards the ends of the ultimate pinna? passing into lobes and 

 teeth ; leaf-substance rather thick ; nerves in the lower pinnules pinnate 

 from a midnerve, with branches forked and simple, those of the lobes up 

 higher forked or simple. 



Locality : Fishing-hut above Dutch Gap Canal ; rare. 



This is a plant with very minute pinnules and lobes, which has the 

 penultimate rachises not winged, and which thus differs from the variety 

 (data. 



Thyrsopteris microlojja, var. alata, sp. nov. 



Plate LV, Fig. 5; Plate LVIII, Fig. 1. 



This differs from T. iiilcroloba mainly in the presence of a wing on 

 the rachises of the penultimate [)iniuie, the smaller size of the principal 



