NO. 2158. JURASSIC FLORA FRO^r ALASKA— KNOW LTON. 453 



reported^ from the Middle Jurassic (Tuxedni sandstone) of Cook 

 Inlet — has thus far been detected in any of the Jurassic areas known 

 in Alaska, though several of the genera are present. To the south, 

 however, tliree species are found to be common to the Jurassic of 

 Douglas County, Oregon, as follows: Pterophyllum rajmahalense, 

 Pterophyllum aequale, Ctenophyllum angustifolium ? 



As these three species occur together at a single locality in the 

 Matanuska Valley, and were not found at any of the other locahties, 

 it is not impossible that they may represent a higher horizon, which 

 would place them more in accord with the Oregon Jurassic. 



The first of these species is reported by Fontaine to be one of the 

 most abundant forms at the Oregoii localities. It was fu-st described 

 from the Rajamahal series of India, in beds believed to be of Liassic 

 age, while the Oregon localities are held to be of the same age as the 

 Jurassic of Yorkshire, England — namely, Lower Oohte. 



The second species (Pteropliyllum aequale) is also one of the abund- 

 ant forms in the Oregon Jurassic. It was first reported in the Rhaetic 

 of Sweden by Brongniart, and later by Nathorst and others. Fon- 

 taine ^ has expressed the opinion that Nathorst has probably con- 

 fused two species imder this name from Sweden, one form of which 

 is the abundant type at the Oregon locahties. 



There is some question about the identification of the third species 

 {Ctenopliyllum angustifolium), and its presence in the rocks of the 

 Matanuska Valley has been queried. The only specimen in the col- 

 lection is the fragmentary one shown in the figure (pi. 80, fig. 2), and 

 while it is smaller than the usual Oregon form shown in Fontaine's 

 figures, it is of the same type and may well have come from near 

 the tip of an especially small leaf. In any event it has been thought 

 better to refer it provisionally to this form rather than found a new 

 species on inadequate material. 



The Matanuska material undoubtedly finds its closest affinity with 

 the material descriljed by Nathorst, Bartohn, Moller, and others from 

 the island of Bomholm, off the southern coast of Sweden, since aU 

 but two of the forms {Pterophyllum rajmahalense and Ctenophyllum 

 angustifolium) are common to the two places. It should be noted 

 that these two species have not been found at the same Alaskan 

 locahties as the other eight species. It is of course true that the 

 identification of two or three of the Matanuska forms has been ques- 

 tioned, but the certainty with which certain of the other forms have 

 been identified makes these doubtful ones the more reasonable. One 

 of the most characteristic and unmistakable forms is the Dictyo- 

 phyllum which genus has been reported but once before from America. 

 Two of the varieties or forms of this species described by Nathorst 

 are also present in the Alaskan material. 



1 U. S. Geol. Sm-vey Bull. 484, p. 64, 1911. 



2 Fontaine, W. M., in Ward, U. S. Geol. Survey Mon. 50, p. 100, 1906. 



