62 CONTRIBUTIONS TO PAL^ONTOLOGY 



In the Medicine Bow coUections there are over 30 fairly complete specimens and several 

 fragments which could have been either segregated into about a dozen species or combined into a 

 single species of somewhat variable leaf form. In view of the intergrading characters of these 

 specimens and their occurrence in great numbers at one horizon of Locahty P. 374, I beUeve it 

 justifiable to refer them to one species. In the references given above, both Lesquereux and 

 Knowlton have admitted that many of the species and varieties hsted were chfficult, if not impossi- 

 ble, to differentiate from the original specimens, referred at that time to Populus nebrascensis. 



The reference of these species to the genus Trochodendroides rather than Populus is based 

 upon the greater resemblance of the leaves to those of several trochodendraceous genera and the 

 occurrence elsewhere of typical seeds and pods of that family in close association with the leaves of 

 this type. Both Berry and Brown liave previously presented adequate evidence for the reference 

 to Trochodendroides} The fossil specimens from the Medicine Bow formation resemble closely 

 the leaves of the hving Tetracentron chinensis Ohver ^ of eastern Asia. 



The stratigraphic and geographic chstribution of the various species of Trochodcndroides, as 

 now conceived, in the Cretaceous and Tertiary deposits of the Rocky Mountain region is still 

 inadequately known. Trochodendroides nebrascensis appears to be most abundant in the lower 

 Denver and lower Medicine Bow formations. Its reported occurrence in the Paskapoo (Fort 

 Union?) of British Cokunbia ' cannot be corroborated because of the lack of figured specimens. 

 Moreover, the Fort Union age of the beds from which the original type specimens were coUected is 

 difhcult to substantiate because of the inadequate description of tlie locahty, which is reported by 

 Newberry ^ as "Banks of Yellowstone River." That the species occurs in the Lance formation is 

 indicated by U. S. National Museum specimens from the "Converse County beds" whicli Knowl- 

 ton tentatively referred to Populus sp.^ My own collection from these same beds east of Lance 

 Creek, Wyoming, contains several leaves which are definitely referable to Trochodendroides nebra- 

 scensis. The species also is present in Ward's coUection of leaves from Black Buttes, Wyoming, 

 which I have consulted at the U. S. National Museum.' 



Though somewhat variable in habit, the leaves liere referred to Trochodendroides nebrascensis 

 are consistent in their ovate shape, rounded or obtuse base, toothed margin, and shghtly narrowed 

 and elongate tip. In these respects they can readily be distinguished from the widespread Fort 

 Union species, Trochodendroides cuneata (Newberry) Berry,' and from others, sucli as Populus 

 anoniala Ward, P. cordata Newberry, P. craspedodronia Ward, P. glandulifera Heer, P. nervosa 

 Newberry, P. newberryi Cockerell, P. richardsoni Heer, and P. speciosa Ward, all of which are 

 reported from the Fort Union formation. The closest resemblance among Fort Union species is 

 with P. daphnogeyioides Ward, which is, however, more narrowly ovate than the average leaf 

 form of Trochodendroides nebrascensis. Pending the final revision of the Fort Union flora by 

 Dr. R. W. Brown of the U. S. Geological Survey, no further attempt can be made to clarify the 

 taxonomic allocation of the numerous leaves of this type. 



Occurrence — Corson Ranch, Wyoming, Loc. P. 372; north of Walcott, Wyoming, Loc. P. 373; 

 Elk Mountain road, Wyoming, Loc. P. 374; Craig, Colorado, Locs. P. 375, P. 376. 



Collection—U. C. Mus. Pal., Plesiotypes Nos. 1336, 1337, 1338, 1339. 



FamiJy MAGNOLIACE^ 



Genus MAGNOLIA Linn^ 



Magnolia lakesii Knowlton 



(Plate 10, Fig. 2) 



Magnolia lakesii Kiowlton, U. S. Geol. Surv. Prof. Paper 130, 142, pl. 13, fig. 2, 1922; Brown, U. S. Geol. 

 Surv. Prof. Paper, manuscript, 1937. 



There are 8 well-preserved specimens in the collections which are referable to this species, 

 which was originally described from the Laramie formation. As indicated above, Brown has 



' Berry, E. W., U. S. Geol. Surv. Prof. Paper 129, 166, 1922; Canada Geol. Surv. Mem. 182, 34, 1935; Brown, R. W.. 

 U. S. Geol. Surv. Prof. Paper, manuscript, 1937; Geol. Soc. Am., Prel. Abstr., 68, Deo. 1937. 

 ' See sheet No. 2156 at The New York Botanieal Garden. 

 •Penhallow, D. P., Rept. Tert. Pl. Brit. Col., 78, 1908. 

 < Newberry, J. S., New York Lyceum Nat. Hist. Annals, vol. 9, 62, 1868. 

 ' Knowlton, F. H., unpublished manuscript, U. S. National Museum. 

 ' See specimen of Populus sp., No. 1149. 

 ' Berry, E. W., Canada Geol. Surv. Mem. 182, 34, 1935. 



