68 CONTRIBUTIONS TO PALiEONTOLOGY 



remote near the apex, consistently parallel, curving only slightly toward the margins where they 

 curve upward more abruptly and run into the margins; secondaries near apex parallehng and 

 curving in toward the midrib; tertiaries fine and very closely spaced, flexuose percurrent, at ap- 

 proximately right angles to the secondaries; very rarely, tertiary branches given off from the lower 

 sides of the secondaries near the margins; finer nervation not observable; margin usually entire, 

 slightly undulate, more rarely with blunt, inconspicuous, upward-pointing teeth near the apex; 

 texture firm. 



The characters of this type of leaf are so easily recognized and consistent that I feel no hesi- 

 tancy in referring Rhamnus brittoni and one specimen of R. rectinervis to the same species. I was 

 at first also incUned to include in it the specimens referred to R. goldiajius,^ but find that in none 

 of my specimens is there any trace of the well-developed branching of the lower secondaries found 

 in that species. Knowlton has remarked upon the similarity of certain specimens from tlie Denver 

 flora referred to Berchemia multinervis (Al. Braun) Heer.^ These are, however, of chfferent shape 

 and do not possess the characteristic upper secondaries parallchng and curving in toward the 

 midrib. In the same report, Knowlton included in Rhavmus cleburni the specimens which 

 Lesquereux had referred to Cornus studeri Heer?. These differ, however, in their more remote, 

 converging secondaries, which are usually forked near the leaf margins. 



As previously recorded, Rhamnus cleburni and the species here included in it are known from 

 the Laramie, Denver, Dawson, Raton, and BLack Buttes floras of the Rocky Mountain region. 

 It is also present in coUections from the Lance of " Converse County," Wyoming, both at Princeton 

 University and the U. S. National Museum. It is not known to occur in the Fort Union floras of 

 western North America, but is reported, though unfortunately not figured, from the Eocene of 

 Oregon' and the Gulf Coast.'' Berry has pointed out "the similarity and possible identity" of 

 the Gulf Coast specimens to the variable leaves of Rhamnus coushatta Berry.'* It is in any event 

 apparent that both the Gulf and West Coast Eocene species are closely related to the late Cre- 

 taceous R. cleburni, indicating a survival of descendant forms in regions outside the Rocky Moun- 

 tain area. 



It is difficult to see any resemblance between the fossil leaves of Rhamnus clehurni and the 

 leaves of modern species of Rhamnus. In my opinion, after consulting herbarium specimens at 

 The New York Botanical Garden, the fossil specimens are not referable to any hving genus of the 

 family Rhamnacese. On the other hand, their leaf characters are closely similar to several genera 

 of the family Dilleniaceaj, namely Davilla, Dillenia, Doliocarpus, and Tetracera. In Dillenia and 

 Tetracera the leaves are usuaUy more regularly toothed along the whole margin than in the fossil 

 specimens. The leaves of Doliocarpus de^Uatus (Aubl.) Standley " of Central and South America 

 are practicaUy indistinguishable in aU details from the fossil specimens. Almost equaUy com- 

 parable are the leaves of Davilla multiflora St. Hil.,' which differ only in their shghtly more obtuse 

 secondaries. Other genera which were consulted but eliminated because of marked differences 

 were Rhamnidium (Rhamnaceaj), Cuphea (Lythraceae) and Meliosma (Sabiaceee). 



Occwrrence— Corson Ranch, Wyoming, Loc. P. 372; north of Walcott, Wyoming, Loc. P. 

 373; Elk Mountain road, Wyoming, Loc. P. 374; Craig, Colorado, Loc. P. 376. 



Collection^V. C. Mus. Pal., Plesiotypes Nos. 1356, 1357. 



Genus ZIZYPHUS Adanson 



Zizyphus hendersoni Knowlton 



(Plate 12, Fig. 6) 



Zizyphus hendeTSoni Knowlton, U. S. Geol. Surv. Prof. Paper 130, 157, pl. 15, figs. 1, 2, 1922. 

 Zizyphus coloradensis Knowlton, ibid., 157, pl. 15, fig. 5. 



There are 5 specimens in the coUections which were at first thought rcfcrable to Ficus 

 planicostata, but which are consistently different in their thinner texture and the presence of 5 



> Lesquereux, Leo, Rept. U. S. Geol. Surv. Terr., vol. 7, 281, pl. 53, figs. 4-8, 1878; Knowlton, F. H., U. S. Geol. Surv. 

 Prof. Paper 101, 332, pl. 101, fig. 4, pl. 112, fig. 5, 1917. 



2 Knowlton, F. H., U. S. Geol. Surv. Prof. Paper 155. 104, 1930. 



> Knowlton, F. H., U. S. Geol. Surv. Bull. 204, 80, 1902. 



* Berry, E. W., U. S. Geol. Surv. Prof. Paper 91, 283, 1916. 

 ' Berry, E. W., U. S. Geol. Surv. Prof. Paper 131, 15, 1923. 

 ' See eheet No. 3748 at The New York Botanical Garden. 

 ' See sheet No. 5359. 



