JlKASSir FLOKA OF lH)l(iLAS CorNTY, (niKd. 77 



can be said is tlint \]io piaiit may be Heer's fossil. The piiuniles are 

 narrowed wediic-sliapc to llic base and seem to have dentate niar<j;ins. 

 The ner\('s are composed of a parent nerve, which sends off very ol)- 

 Hquely laleial nerves. The teeth on the mariiin seem to be acute and 

 very obTKjnely })hiced, being mostly on the anterior niarijin of the 

 pinnules. 



Vv^. 9 represents one of the specimens, Fig. 10 a portion enlarged, 

 and Fig. 11 shows what seems to have Ijeen the original form of the 

 pinnules. 



Genus T.ENIOPTERLS Bn>iit,'niart. 



Forms like Ta-niopteris are more common in tlie Oregon Jurassic 

 flora than the ferns with smaller pinnules. 1 shall use the distinction 

 suggested by Xathorst as an essential one between Tamiopteris and the 

 vmsegmented Xilsonias that, in shape, so much resemble Ta^niopteris. 

 This distinction is that the lamina of Taniiopteris is attached to the 

 side of the midrib and in Xilsonia to the upper surface. This feature 

 causes a Tjeniopteris to show a distinct midrib, whether the upper or 

 the under surfac(> be presented uppermost. In the case of Nilsonia, 

 however, when the upper surface is seen uppermost there is no visible 

 midrib or axis. The nerves l^elonging to the lamina on opposite sides 

 of the axis meet in a raised cord in the center of the position that would 

 be occupied by the midrib if it were shown. But if the lower surface of a 

 Nilsonia be presented uppermost the axis or midrib is seen, and, therefore, 

 while the absence of a distinct midrib may be taken as showdng that the 

 plant is a Xilsonia, yet, in cases where a midrib is shown, one can not be sure 

 that the plant is not a Nilsonia with its imdei' surface presented uppermost. 



There are in the Oregon collection a number of leaves that in their 

 shape are like TaMiiopteris. The}- are, however, never seen with their 

 lamina" di\-i(led or segmented. They show no mitlrib, but have their 

 lateral nerves meeting in a raised cord that occupies the central line 

 of the position that would l)e occupied by the midrib if it were present. 

 These leaves have uniformly in their laminae a thin texture. In some 

 the lateral nerves are always single and show no thickening toward 

 their bases near their insertion on the central cord. Others, with the 

 same unchanged thickness in the lateral nerves, have them rarely forked, 

 but in such way as to show that the essential character here, too, is an 



