150 



LARAMIE FLORA OF THE DENVER BASIN. 



Garden, is based upon the several examples 

 figured. In the larger specimen (fig. 10) the 

 whole leaf is about 12 centimeters long, in- 

 cluding the petiole, which is 3.5 centimeters 

 long. The terminal leaflet appears to have 

 had a petiole fully 2 centimeters long, and the 

 blade is about 6 centimeters long and 5 cen- 

 timeters broad. The lateral leaflets have 

 petioles only about 4 millimeters long. The 

 one wholly preserved is 5 centimeters long and 

 3 centimeters broad. The nervation is ob- 

 scure, and it is possible to make out only a few 

 of the secondaries. 



The genus Negundo 29 — if it is to be main- 

 tained as distinct from Acer — is represented by 

 three living species, with a number of more or 

 less well-marked varieties, and is entirely 

 North American in distribution. 



Up to the present time about eight fossil 

 species of Negundo have been described, of 

 which three are European and the remainder 

 American. Of these the oldest is Negundo 

 (or Negundoides) acutifolia (Lesquereux) Pax, 30 

 from the Dakota sandstone of Kansas and 

 Nebraska, which differs in having thin lanceo- 

 late leaflets, obscure as to their point of attach- 

 ment. The next younger species is N.decur- 

 rens Lesquereux, 31 from the Denver formation 

 at Golden, Colo. This species rests upon a 

 single specimen which has not been figured, 

 but it is regarded by Lesquereux as being 

 closely allied to N. triloba Newberry, 32 a species 

 found only in the Fort Union near the mouth 

 of Yellowstone River in Montana. Negundo 

 triloba is evidently closely related to the living 

 box elder (N. aceroides) and differs from N. 

 brittoni, the one here described, in having the 

 terminal leaflet smallest and in all being 

 coarsely toothed. 



» There has been much discussion as to the propriety of maintaining 

 Negundo as a separate genus, and it is probable that the grounds tor so 

 doing are inadequate from the botanist's point of view. The box elders 

 appear to be most closely related to the red maples, with which they 

 agree in having the flowers appearing before the leaves, and these two 

 types are separated from other maples by having compound instead of 

 lobed leaves. If the possession of compound leaves was confined to this 

 group ( Negundo) it might be best to consider them generically separate 

 from Acer, but there is another, otherwise unrelated group of Chinese 

 and Japanese species withternate leaves. For paleontologic purposes 

 it has been thought best to retain the box elders under Nepimdo, though 

 recognizing full well the fact that the basis for this action is not very 

 secure. 



*> Pax, F., in Engler's Bot. Jahrb., vol. 6, p. 356, 1885. Lesquereux, 

 Leo, The Cretaceous flora; U. S. Geol. Survey Terr. Rept., vol. 6, p. 97, 

 pL 21, fig. 5, 187^. 



a Lesquereux, Leo, Harvard Coll. Mus. Comp. Zoology Bull., vol. 16, 

 p. 54, 1888. 



82 Newberry, J. S., TJ. S. Geol. Survey Mon. 35, p. 115, pi. 31, fig. 5, 1898. 



The only other American species, from the 

 Mascall formation of the John Day Basin, 

 Oreg., was described under the name Rulac 

 crataegifolium Knowlton 33 when it was thought 

 that Rulac was the tenable name for replacing 

 Negundo. This species also rests on a single 

 rather fragmentary specimen and, if correctly 

 interpreted, has the terminal leaflet much 

 smalFer than the lateral ones ; both are sharply 

 toothed. 



The European forms are N. bohemicum 

 Menzel, 34 Yrom the Oligocene of Sulloditz, 

 Bohemia, and N. europaeum Heer 35 and N. 

 trifoliata (Al. Brau'n) Al. Braun, 38 from the 

 Miocene of Oeningen, neither of which ap- 

 roaches closely our species. 



In North America we have the following 

 species, which, when arranged in ascending 

 geologic order, exhibit what we now know of 

 the development of the genus: 



Negundo acutifolia (Les- 

 quereux) Pax Dakota sandstone. 



Negundo brittoni Knowl- 

 ton, n. sp Laramie formation. 



Negundo decurrens Les- 

 quereux ". Denver formation. 



Negundo triloba Newberry. .Fort Union formation. 



Negundo crataegifolia 

 (Knowlton) Knowlton, n. 

 comb Miocene. 



Negundo aceroides Moench. .Living. 



Occurrence: Laramie formation, Marshall, 

 Colo. 



Family SAPINDACEAE. 



Pistacia eriensis Knowlton, n. sp. 



Plate XXVIII, figures 1-4. 



Pistacia eriensis Knowlton [nomen nudum], U. S. Geol. 

 Survey Bull. 696, p. 460, 1919. 



Leaf compound, imparipinnate, tri(?) -folio- 

 late; rachis slender; leaflets arising from the 

 same point, the terminal one short-petioled, 

 the lateral ones sessile; leaflets oblong-lanceo- 

 late, acuminate at the apex, the, terminal one 

 with a wedge-shaped base, the lateral ones in- 

 equilateral in the upper side, all entire; midrib 

 of leaflets rather strong; secondaries numerous, 

 14 to 20 pairs, mainly opposite or subopposite, 



" Knowlton-, F. H., U. S. Geol. Survey Bull. 204, p. 77, pi. 16, fig. 7 

 1902. 



« Naturw. Gesoll. Isis, Bautzen, Sitzungsb. und Abh., 1896-97, p. 52, 

 pi. 2, figs. 8-9. 



» Heer, Oswald, Flora tertiaria Helvetiae, vol. 3, p. 60, pi. 118, figs 

 20-22, 1869. 



3« Bruokmann, Dr., Ver. vaterl. Naturkunde Wiirttemberg Jahresb. 

 VI. Jahrg., p. 235, 1850. 



