158 



LARAMIE FLORA OF THE DENVER BASIN. 



several secondary branches on the outside; 

 lower or outer pair of ribs slightly more slender 

 than the others, passing up for nearly or quite 

 half the length of the blade, each with five or 

 six secondary branches on the outside which 

 arch forward and disappear just inside the 

 margin; nervilles numerous, strong, mainly un- 

 broken, and at right angles to the ribs or 

 secondaries. 



This form is represented by a number of ex- 

 amples, of which the two best preserved are 

 here figured. The specimen that is most nearly 

 perfect in outline is shown in figure 2. It is 

 about 9 centimeters long and 5.5 centimeters 

 wide. The nervation shows only the ribs and 

 some of the secondaries, the nervilles being ob- 

 scure or effaced. The other specimen (fig. 1) 

 comprises only the base of a leaf of about the 

 same size as the one seen in figure 2, but the 

 nervation is much better preserved. The origin 

 of the outer pair of ribs is very well shown in 

 this specimen — that is, they are seen to arise 

 as branches from the inner pair of ribs, thus 

 being virtually secondaries. Each gives rise to 

 some five or six branches on the outside. The 

 nervilles and their disposition are well shown 

 in the figure. 



This fine species most closely resembles 1 

 Zizyphus fibrillosus (Lesquereux) Lesquereux, 52 

 a species well known in the Denver and Raton 

 formations. From this it differs essentially in 

 having the base distinctly wedge-shaped in- 

 stead of truncate or heart-shaped. The man- 

 ner in which the principal' ribs arise is the same 

 in both species — that is, they are essentially 

 three-ribbed with the lateral and basal second- 

 aries arising just above the base and by then- 

 strength simulating ribs. The nervilles in the 

 present species are similar to those in Zizyphus 

 fibrillosus except that they are neither so nu- 

 merous nor so regular. 



I take pleasure in naming this species in 

 honor of Judge Junius Henderson, curator of 

 the museum of the University of Colorado, 

 Boulder, Colo. 



Occurrence: Laramie formation, in cut in 

 clay beds about 1 £ miles south of Golden, Colo., 

 collected by A. C. Peale, 1908; Cowan station, 

 10 miles south of Denver, Colo., collected by 

 F. H. Knowlton. 



" Lesquereux, Leo, The Tertiary flora: V. S. Geol. Survey Terr. Kept, 

 vol. 7, p. 276, pi. 52, figa. 1-6, 1878. 



Zizyphus corrugatus Knowlton, n. sp. 



Plate XVII, figure 3. 



Zizyphus corrugatus Knowlton [nomen nudum], U. S. Geol. 

 Survey Bull. 696, p ; 660, 1919. 



Leaf apparently rather thick in texture, ovate, 

 with abruptly rounded, truncate or slightly 

 cordate base and obtusely pointed apex; seven- 

 ribbed from the top of the petiole, the midrib 

 strong, straight, with two pairs of alternate 

 secondary branches in the upper part; next 

 pair of ribs at an angle of about 80°, passing 

 to the upper margin, each with three or four 

 secondary branches on the outside ; next outer 

 pair of ribs at an angle of about 60°, reaching 

 the margin below the middle of the blade, each 

 with two or three secondary branches on the 

 outside; lower pair of ribs at an angle of about 

 30°, apparently without secondary branches: 

 nervilles thin, few, usually unbroken. 



The leaf figured, which is nearly perfect, is 

 about 8.5 centimeters long and about 5 centi- 

 meters wide and is very well characterized. 

 This form is in some ways more closely related 

 to Zizyphus fibrillosus Lesquereux 53 than Zizy- 

 phus hendersoni, the form just described. It 

 differs, however, in being more broadly ovate, 

 in having the ribs nearly or quite straight in- 

 stead of curved, and above all in the character 

 of the nervilles which is much the same in 

 both and is wholly unlike that of Zizyphus 

 bfirillosus. 



Occurrence : Laramie formation, Cowan sta- 

 tion, 10 miles south of Denver, Colo., collected 

 by F. H. Knowlton. 



Zizyphus minutus Knowlton, n. sp. 



Plate XVIII, figure 1. 



Zizyphus minutus Knowlton [nomen nudum], U. S. Geol. 

 Survey Bull. 696, p. 661, 1919. 



Leaf of small size, probably about 3.5 centi- 

 meters in length and 8 millimeters in width, 

 apparently coriaceous, linear-lanceolate, nar- 

 rowly wedge-shaped at the base (apex de- 

 stroyed); three-ribbed from the extreme base 

 of the blade, the ribs nearly equal in strength, 

 the lateral ones passing well up to the apex; all 

 finer nervation obscure or effaced. 



Although this species is based on a single 

 specimen, which lacks all of the apical portion, 



a Lesquereux, Leo, The Tertiary flora: TJ. S. Geol. Survey Terr. 

 I Bept., vol. 7, p. 276, pi. 52, figs. 1-6, 1878. 



