102 DESCRIPTION OF SPECIES. 



No. 13, all have simple, more or less acute, more or less distant teeth; 

 and the lateral veins all simple, straight, craspedodrome, vary in nothing 

 but in their more or less acute angle of divergenoe according to the width 

 of the leaves; the petiole is equally variable, from 5 to 10 millimeters 

 long, and the leaves are sometimes nearly sessile, as in fig. 7. One of the 

 leaves of fig. 1 has also the petiole very short. Comparing the different 

 forms of figs. 14-27 we see the same essential characters preserved — that 

 is, lateral veins straight, craspedodrome, at a more or less acute angle of 

 divergence relatively to the width of the leaves, the teeth either sharply 

 acute, even acuminate, or merely pointed, even obscurely so, as in figs. 

 -'>. 27. The petiole is generally of the same length, but some of the leaves 

 (figs. 21, 26, 27) are narrowed to the base and nearly without petiole. 

 If I add that all these leaves have the same consistence and black color 

 upon the shale, that both forms are often found upon the same specimens, 

 that it is often scarcely possible to say that a leaf is referable to the nor- 

 mal type or to the variety, it will be understood why I am unable to con- 

 sider these leaves as representing different species or referable to two 

 genera, though, comparing the extreme forms (figs. 1, 5, 6, to figs. 21, 24, 

 27), this separation seems indeed natural. 



As for the identity of this species with P. Ungeri, it is disproved by the 

 comparatively large and narrower leaves, the veins, exactly straight from 

 the medial nerves to the point of the teeth, never curved, and the fruits 

 which, as seen in comparing fig. 12 with fig. 1, pi. lxxx of Heer, "Fl. Tert. 

 Helv.," are nearly twice as large in the American species. The difference 

 in the characters of the leaves may be easily seen in comparing the figures 

 of pi. xxix with that of P. Ungeri, quoted below. 



Hob. — Florissant. Most abundant. 



Planera Ungeri, Ett. 

 "U. S. Geol. Rep.," vii, p. 190, pi. xxvii, 8g.7. 



