296 MESOZOIC FLORAS OF UNITED STATES. 



Immediately after leaving the rachis the bundle splits up into about three 

 principal branches, and these branch again several times, the entire group 

 diverging flabellatel}^ so as to fill the pinnule. The nervation then is much 

 like that of the Acrostichites of the Older Mesozoic flora of Virginia. It 

 may l^e compared with that of A. microphyllus Font., a plant which is a 

 good deal like the one now in question and which was described in Mono- 

 graph United States Geological Survey, Vol. VI, page 33. 



The nervation of the inferior basal and flabellate pinnules is conformed 

 to the shape of these pinnules. It consists of a nerve bundle which splits 

 into three main branches, one of which goes into each lobe of the pinnule, 

 giving off diverging and forking branches which fill each lobe. In the less 

 commonly occurring abnormal forms there is some variation from the type 

 shown in both the basal inferior pinnules and in those on the other portions 

 of the ultimate pinnae. The basal inferior pinnules are less deeply lobed 

 than those on the pinnae with normal pinnules, more elliptical in shape, and 

 strongly deflexed along the rachis of the penultimate pinnae. They are 

 either elliptical or spatulate in form. 



The other pinnules of these forms are mostly larger than the normal 

 ones. They are ovate to elliptical in shape, obtuse to subacute, rounded 

 off at base on both the lower and the upper side, owing to an abrupt nar- 

 rowing of the pinnule immediately at its attachment to the rachis of the 

 pinna. Some of the forms that are subacute are sometimes even acumi- 

 nate from the gradual narrowing of the pinnules toward their tips. The 

 nerves in all the pinnules of the abnormal forms are of the same type as 

 those of the corresponding ones on the normal forms, but the nerves of the 

 more common pinnules are apparently thicker and more vaguely defined 

 than those of the corresponding normal ones. 



PL LXXI, Fig. 21, represents a penultimate pinna, carrying portions of 

 several ultimate pinnae, which well show the small pinnules that constitute 

 the normal forms, and also their accompanying basal pinnules. Fig. 22 

 gives two of the normal pinnules magnified four diameters, to show the 

 nervation. Fig. 23 represents a portion of a pinna of the abnormal kind, 

 containing the largest pinnules found, and Fig. 24 gives a part of a primary 

 pinna of the abnormal kind, which carries portions of three ultimate 

 pinnae, showing well the form of the more acute pinnules of this kind, and 

 also portions of their accompanying basal deflexed pinnules. The nerves 



