FOX HILLS AND LOWER MEDICINE BOW 67 



beeoming indistinet close to the leaf borders; tertiaries thin, percurrent at angles approachinp; 90° 

 to tlie plane of the midrib; finer nervation not prcserved; margin entire throuKhout; texture firm. 



This species appears to be most abundant in the Laramie and Medicine Bow formations. 

 It is evidently lcss abundant though definitely present in thc Vermejo and Black Buttes fforas, 

 and is questionabiy idcntified in the Denver and Dawson floras. Its reported occurrence in the 

 Lance formation ' seems likeiy, thouRh as yet unsubstantiatcd by fisured specimens. To my 

 knowledge tliere are no reported occurrences of leaves of this type from formations of indisputable 

 Paleocene or later age. 



The leaves of this fossil spccies are, in my opinion, distinctly not rhamnaceous. I have 

 studied all available hcrbarium material of the genera of the Rhamnaceie at The New York 

 Botanical Garden and failed to find a comparable leaf type. Scveral genera of the Lauracctc, on 

 the other hand, are very simiiar in most details. Persea lanceolata has leaves of the same general 

 shape and venation. Even closer are the leaves of Nectandra pichurim (H.B.K.) Mez.,' of 

 northern South America, and A''. memhranacea (S.W.) Griesb.,' of Central America, which possess 

 the same well-defined secondary and tertiary venation and the same variations in size and shape 

 as the fossil specimens. 



Occurrence — Cor.son Rancli, Wyoming, Locs. P. 371, 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. 1353, 1354, 1355. 



Rhamnus cleburni Lesquereu.\ 

 (Plate 14, Figs. 5, 6) 



Rhamnus clehurni Lesquereux, U. S. Geol. Surv. Terr., 6th Ann. Rept. (1872), 381, 400, 1873; Rept. U. S. 



Geol. Surv. Terr., vol. 7, 280, pl. 53, figs. 1-3, 1878; Berry, U. S. Geol. Surv. Prof. Paper 91, 283, 1916; 



Knowlton, U. S. Geol. Surv. Prof. Paper 101, 332, pl. 113, fig. 3, 1917; idem, Prof. Paper 15.5, 104, only 



pl. 46, figs. 10, 11, 1930. 

 Rhamnus reciinervis Heer (in part). Lesquereux, U. S. Geol. and Geog. Surv. Terr., Ann. Rept. (1871), 29.5, 



298; idem (1872), 382, 397, 402, 1873; idem (1873), 405, 1874; Rept. U. S. Geol. Surv. Terr., vol. 7, 278, 



pl. 52, fig. 15 only, 1878. 

 Rhamnus hrilloni Knovvlton, U. S. Geol. Surv. Prof. Paper 130, 156, pl. 15, fig. 6, pl. 24, fig. 8, 1922. 



This type of leaf is one of the more abundant and widespread in the Medicine Bow collections. 

 It is remarkably consistent in the majority of its observable characters, being particularly so in 

 its secondary and tertiary venation. The average leaf specimen is identical with the original type 

 specimens of Rhamnus cleburni from the Denver formation. In studying the large number of 

 leaves of this type in my collection, however, it has become apparent that the leaves are somewhat 

 more variable, as one would expect, than Lesquereux's description and figures might imply. The 

 two specimens here figured were chosen to show such variations rather than the average type. In 

 figure 5, for example, is shown a somewhat more lanceolate leaf than the average, whose upper 

 margin is invested with short, blunt, upward-pointing teeth, identical with those seen in Les- 

 quereux's figure of Rhamnus rectinervis. The largest specimen obtained is shown in figure 6. This 

 is somewhat wider above the middle than the average form, and has a more elongate tip; otherwise 

 it is precisely the same. In view of the range of variations now known it seems desirable to re- 

 describe the species as here conceived. 



Description {Supplementary) — Leaves oval or elliptic, more rarely lanceolate, the shghtly 

 unequal base narrowly to broadly cuneate, rarely rounded, and the apex acute or slightly extended 

 into an acuminate tip; average dimensions about 11 cm. by 4.5 cm., ranging up to 17 cm. by 9 cm.; 

 minimum size observed in collections 7 cm. by 4 cm.; petiole stout, relatively long, up to 3 cm.; 

 midrib straight, heavy except near the apex where it becomes thin and occasionally undulating; 

 9 to 15 pairs of prominent secondaries, subopposite to alternate, leaving the midrib at angles 

 consistently from 40° to 45° except near the apex where they become more acute; rarely the basal 

 pair are slightly less acute; secondaries closely and evenly set along the niidrib, becoming more 



1 HoUick, A., in Brown, B., Am. Mus. Nat. Hist. Bull., vol. 23, 823-845, 1907; Knowlton, F. H., Washington Acad. 

 Sci. Proc. vol. 11, 18.5, 1909. 



» See sheets No. 1396 and No. 4323, New York Botanioal Garden. 

 ' See sheets No. 987 and No. 169, New York Eotanical Garden. 



