DESCRIPTION OP SPECIES. 67 



Pterophyllum decussatum. 

 Plate XLIII, Fig. 2. 

 Pterozamites decussatns, Emmons. Am. Geol., plate iii, fig. 1. 



The small fragment of this plant figured on Plate XLIII, Fig. 2, was 

 found in the Cumberland Area in the black shale occurring on the horizon 

 of the coal beds. It seems identical with the fossil found by Emmons in 

 the Mesozoic strata of North Carolina, and called by him Pterozamites de- 

 cussatns. The only point of difference is the slight narrowing of the leaflets 

 towards their base and their slight expansion immediately at their base. 

 These are points that serve to unite this plant closely with the Pterophyllum 

 longifolium of Andrae, P. Andrceanum of Schimper, from the lower Lias of 

 Steirdorf. The chief difference is the smaller size of the leaflets of P. decus- 

 satum. It is also much like P. longifolium, Brgt., from the Trias. The 

 nerves are simple from their insertion, and parallel to one another and to the 

 margin of the leaflets. The middle nerves of the leaflets stand at right 

 angles with the midrib, while the nerves nearer the sides of the leaflets are 

 slightly oblique at their insertion. Only a small portion of the midrib is 

 shown at the base of the leaflets. 



CTENOPHYLLPM, Schimper. 



Leaves linear; leaflets attached obliquely to the upper side of the midrib, more 

 often opposite, linear, obtuse, decurrent at base, coriaceous, with delicate and parallel 

 nerves. 



Schimper has separated all the plants with the above features from the 

 genus Pterophyllum. The true Pterophylla are perhaps more abundant in 

 the Triassic than in any other formation, while the Ctenophylla are espe- 

 cially characteristic of the Rhaetic and Lias. 



Ctenophyllum taxinum, (Lindl and Hutt. spec.) 



Plate XXXIII, Figs. 2 to 4. 



Leaves linear ; midrib strong; leaflets obliquely and closely placed, separate to 

 the base in the lower leaflets, and united at the very base in the upper ones, either 

 straight and of the same width to the ends, and there obliquely and bluntly rounded 

 off, or slightly falcate, and narrowed towards the summits, and then obliquely rounded 

 off; 12 millimeters long and 2 millimeters wide. Nerves very fine, parallel to each 

 other and single. 



