DESCRIPTION OF SPECIES. 71 



the fine specimen given in Fig. 1. The lower leaflets of the leaf are usually 

 irregular in every way. They are more apt to be remotely placed than 

 those of the middle and upper part of the leaf, and also to be abnormally 

 wide and thick at base, to be shorter than the normal length, and to stand 

 nearly or quite at a right angle to the midrib. Plate XXX IV, Fig. 4, and 

 Plate XXXVII, Fig. 2, represent such portions of the lower part of the leaf. 

 Plate XXXIV, Fig. 4 a, gives the nervation of enlarged leaflets of Fig. 4. 

 Plate XXXIV, Fig. 2, gives another form of the basal portion of a leaf, 

 where the leaflets are closely placed and falcate, but much shorter than 

 usual. The leaflets of the middle portion of the leaf, such as those repre- 

 sented in the lower part of Plate XXXVII, Fig. 1, and in Plate XXXVIII, 

 Fig. 2, which is a fragment of a smaller leaf, go off at an angle of about 

 45° and are usually slightly curved upward towards the summit of the leaf. 

 They here, as well as toward the summit of the leaf, are widest at base, and 

 diminish in width almost imperceptibly until the tip of the leaflet is reached; 

 here the leaflet is rounded off bluntly with an elliptical outline. The tips 

 almost never are to be seen, since they are destroyed in the compression of 

 the plant in the shale. The bases of the leaflets are thickened and rigid for 

 some distance above the insertions. The part of the midrib upon which 

 the bases of the leaflets rest is thickened, as represented in Plate XXXIV, 

 Fig. 4, and Plate XXXVII, Figs. 1, 2. It forms a marginal line on each 

 side of the midrib on its upper surface. The upper surface within these 

 lines is irregularly striate and flat, but we sometimes find the stem traversed 

 by two or three furrows or grooves besides the markings above mentioned. 

 The lower surface of the midrib is usually smooth, cylindrical, and promi- 

 nent, as in Plate XXXVIII, Fig. 2. The midrib tapers gradually from the 

 lowest portion generally to the summit, where near the base of the terminal 

 leaflet it is suddenly narrowed. Sometimes, however, the sudden attenuation 

 takes place some distance below the summit, and then the tapering is 

 gradual, until at the summit the midrib is abruptly terminated. The upper- 

 most leaflets become more and more oblique in their insertion, and are 

 usually united more or less at their bases. In the middle portions of the 

 leaf their bases usually touch without being united, while in the lower basal 

 portions they are often quite far apart. 



