120 MESOZOIC FLORAS OF UNITED STATES. 



leaf substance. This indicates that the nerves are disclosed only on 

 the lower surface. The nervation resembles that of Neuropteris of 

 the Carboniferous, but there is no midnerve visible, although it may 

 be present, as the nervation is not fully disclosed. The nerves appear 

 to radiate from the base of the fossil, and they fork several times. The 

 surface of the coal film, which represents the supposed bract, is granu- 

 lated with minute papillse of no definite form. They may.be due to 

 the shrinking of the leaf. The general aspect of these fossils suggests 

 that they may be bracts of the involucre of some Williamsonia. The 

 three found are apparently essentially the same, but present some unim- 

 portant differences in form, which are shown in the figures given. They 

 are distinguished as a, b, c. 



Bract a is elliptical in form and not symmetrical, one lateral margin 

 being more strongly convex than the other. It tapers gradually to a 

 subacute tip,, which is well shown. The base is imperfect. Bract b 

 is of the same general form, but is broader and proportionally shorter. 

 The basal portion is wanting. Bract c is ovate elliptical and nearly 

 symmetrical in form. 



PI. XXIX, Fig. 8, represents bract a, enlarged in Fig. 9; Fig. 10 

 bract h, and Fig. 11 bract c, enlarged in Fig. 12. 



Order GINKGOALES. 



Family GINKGOACE^. 



Genus GINKGO Kaempfer. 



The Ginkgos of the Oregon Jurassic are the most important fossils 

 in it. This is due to the fact that they show a great number of speci- 

 mens and a very considerable variety of forms, which are quite well 

 preserved. The leaves are preserved mostly entire, and the condition 

 in which they may be obtained depends on the splitting of the i-ock 

 containing them. Unfortunateh^ the cleavage of this is generally poor, 

 otherwise verj^ perfect specimens might be obtained in greater num- 

 bers. At some of the localities the imprints of Ginkgo leaves are 

 exceedingly numerous and may be obtained bj^ the hundreds. The 

 faces of the rock, when exposed by splitting it, are covered with numer- 

 ous impressions, often of different character or type, while the variation 

 in the leaves is considerable. I am not sure that they are not all modi- 



