292 MESOZOIC FLORAS OF UNITED STATES. 



The nervation varies with the pinnules. It is very distinct and 

 sharply defined. In this respect it surpasses that of the forms of this 

 species found in the Potomac formation of Virginia. As stated, the 

 long crenate pinnules were not seen attached, but in the normal pin- 

 nules with entire margins the midnerve leaves the rachis at an acute 

 angle and enters the pinnule near its lower basal margin, so as to divide 

 the lamina into unequal parts. It becomes very gradually attenuated, 

 and, as is the case with Cladophlebis, splits up at its end into several 

 branches. The lateral nerves of the normal pinnules, although dis- 

 tinct, are rather slender. They go off very obliquely from the midrilD 

 and curve outward toward the margin of the pinnules. They fork 

 near their insertion, and each branch forks again at about the middle 

 of the lamina, while the branches continue nearly parallel to one another 

 until they meet the margin. This nervation reminds one of that of 

 the small-pinnuled neuropterids of the Paleozoic. The basal nerve 

 bundle on -each side of the midnerve is inserted, not on the midnerve, 

 but at the point of its attachment to the rachis of the pinna. 



The lateral nerves of the long crenate and of the lobed pinnules 

 form nerve bundles that go off obliquely from a common point of inser- 

 tion and are composed of several branches, which in turn split up into 

 others, the whole group diverging flabellately and curving away from 

 the midrib to meet the margin at a large angle. These nerves are rather 

 coarse. The nerve bundles fill the lobes and crenate incisions. All 

 the lateral nerves, in every part of the plant, are noteworthy for the 

 length of the l^ranches into which they split up. In the pinnules toward 

 the ends of the pinnae and in the upper part of the frond the lateral 

 nerves are forked only once. 



This fine fern is one of the most abundant fossils in the Geyser 

 group of strata and it is the best preserved. A large number of impres- 

 sions of good size and belonging to different portions of the plant have 

 been found. In these we find some features different from the character 

 of C.falcata, as made out from the fossils of the Potomac beds of Virginia." 



It may be questioned whether or not these forms show enough 

 difference from the species of the Virginia Potomac to justify their 



a Potomac Flora (Monogr. U. S. Geol. Surv., Vol. XV), pp. 72, 73, pi. iv, fig. 8; pi. Vjfigs. 1-6; pi. vi^ 

 fig. 7; pi. vii, figs. 1, 2. 



