38 THE OLDER MESOZOIC FLORA OP VIRGINIA. 



principal rachis, while none are ever found on the deflexed heteromorphous 

 pinnule. They become more numerous in the pinnules and more regularly 

 placed as they depart from the main rachis. They are most numerous on 

 the pinnules of the lower pinnae, and diminish in number in the pinnules of 

 the upper pinnae, where they often become very few and even single, and 

 are scattered irregularly on the pinnules. These features are well shown in 

 Plate XVI, Fig. 1, where we have only single sori in the uppermost pin- 

 nules, and also in Plate XVIII, Fig. 1, where they are seen to diminish in 

 number on the pinnules toward the principal rachis. On by far the greater 

 number of fructified plants the sori occupy only the lower half of the pin- 

 nules, and then the nerves are plainly to be seen in the ends of the pinnules. 

 This feature is shown in Bunbury's figure. Plate XVI, Fig. 1 a, represents 

 a pinnule not fully fructified, where the tips are free from sori. They are 

 the magnified pinnules of Fig. 1. More rarely we find the pinnules fully 

 fructified and bearing sori to the summit, as represented in Plate XVIII, 

 Fig. -2. These pinnules are narrower and more elongate than the partially 

 fructified pinnules represented in Plate XVI, Fig. 1. The nerves here are, 

 so far as seen, only in the form of pedicels bearing the sori, while the pin- 

 nules represented in Plate XVI, Fig. 1 a, show that the sori are borne on a 

 lower branch of the lateral nerves. The sori appear somewhat differently, 

 according to the manner in which the imprint has been formed. Very often 

 they appear as raised globose prominences which, under a strong lens and 

 when exceptionally well preserved, show the compound nature of the sorus. 

 In other cases they appear as pits rounded in shape, with a central circular 

 depression, caused by the axis. In this form they are represented in Plate 

 XVI, Fig. 1 a. When the structure can be made out, the sori are seen to 

 be composed of five or six sporangia ranged around an axis, as seen in Plate 

 XVIII, Fig. 2 a, which represents a fully fructified pinnule of Fig. 2. Here 

 the nerves are obliterated, or at least cannot be made out, except the basal 

 portions of the lateral nerves, which attach the sori to the middle nerve. 



The fructification of this plant resembles that of Laccopteris but the 

 frond is not digitately divided, as in that genus. Plate XVIII, Fig. 1, rep- 

 resents the lower portion of a large specimen in which the pinnules are 

 crenately lobed. Plate XV, Fig. 3, represents a pinna from a similar por- 



