144 EXPLORING EXPEDITION FROM SANTA Fl 



once-forked ; sori from 1 to 5 on basal portion of pinnules, seated on the nerves, and 

 apparently covered with an indusium. 



This is an exceedingly neat and pretty species, quite distinct from-any other with 

 which I am familiar. The plant was evidently small, and the fronds very delicate 

 and membranous. 



In common with most of the smaller Mesozoic species of the genus, it had long, 

 narrow, riband-like pinna-, and pinnules more or less falcate. In the form of the 

 pinnules, the plant resembles Pecopteris+Wliitbiensis, but the nervation is less crowded, 

 the pinnae more elongated, and in size the one is biit a miniature of the other. 



Formation and locality. Triassic shales ; at the Coal-mines of Los Bronrcs, 

 Sonora (Mr. Remond). 



PECOPTERIS FALCATUS, Emmons. 



Plato VI, fig. 3. 



This is evidently the plant described by Professor Emmons (Geol. N. Carolina, 

 p. 327, fig. 9) as the fertile frond of his P. falcatus. No specimens of the barren 

 frond occur in the collection; but the resemblance of the plant before us to that 

 represented in the figure to which I have referred will be apparent to any observer. 



Professor Heer considers P. falcatus of Emmons as identical with Laccoptcris 

 f/crminans Goep. (Gatt. Foss. Pflanz. liv. 1 and 2, plate vi, fig. 8) from the Keuper of 

 Bayreuth ; and he is probably correct in that -conclusion, but the want of sterile 

 fronds in the collection made by Mr. Remond leaves this question as it was, and we 

 are now only able to identify, by means of this and the other species common to 

 these widely-separated localities, the plant-beds of Sonora with the Trias of North 

 Carolina and Richmond. 



Formation and locality. Los Bronces, Sonora (Mr. Remond). 



PTEROPHYLLUM FRAGILE, Newb. 



Plate VI, figs. C and f.. 



Plant apparently delicate and fragile; midrib of frond slender and weak; pinnules 

 oblong on the center of the frond, quadrangular above and below; summit squarely 

 truncated; base attached to the rachis by its entire width; nerves fine, straight, simple, 

 parallel. 



The figure now given of the central part of the frond is taken from the only spe- 

 cimen which shows distinctly the nervation and other diagnostic characters of the 

 species. In this the midrib is very delicate, and the pinnules are given off at a right 

 angle. The other figure (G a ), which represents the base of a frond, is taken from a 

 specimen which may belong to another species, as the nervation is nearly obliterated, 

 and the pinnules are given off at an acute angle. I have thought it probable, however, 

 that this latter peculiarity was simply due to their position near the base of the frond. 

 With this exception, there is no tangible difference. Should this be found to be a con- 

 stant feature, however, it would make it necessary to establish a new species on the 

 specimen represented in fig. 6. 



Formation ami locality. Triassic strata; Los Bronces, Sonora, Mexico. 



