58 MESOZOIC FLORAS OF UNITED STATES. 



enlarged. Fig. 5 gives terminal portions of two penultimate pinnae 

 carrying sterile pinnules, with entire margins (entire pinnules), and 

 hence they come probabh' from high up on the compound pinna. PL 



VI, Figs. 6 and 7, represent magnified pinnules to show details. PI. VI, 

 Fig. 8, represents portions of penultimate pinnae, with fertile entire 

 and dentate pinnules, that probably nearly correspond in position with 

 the sterile parts giyen in Fig. 5. PI. VI, Fig. 9, shows an enlarged pin- 

 nule of Fig. 8 with sori. PL VII, Fig. 1, gives a portion of a penulti- 

 mate pinna with ultimate pinnae carrying sterile pinnules having 

 crenately dentate margins. These pinnules are distorted somewhat 

 by being pressed down into the rock. PL VII, Fig. 2, shows a fragment 

 of a penultimate pinna carrying ultimate pinnae having very small 

 fertile pinnules with crenate margins. This presents the upper sur- 

 face of the plant uppermost, so that the sori are seen through the leaf 

 substance. PL VII, Fig. 3, shows an enlarged pinnule of Fig. 2. PL 



VII, Fig. 4, gives a fragment of a penultimate pinna with portions of 

 ultimate pinnae carrying sterile lobed pinnules from pretty low down 

 on the compound pinna. These are of the largest size, being lobed 

 and tending to pass into ultimate pinnae. PL VII, Fig. 5, shows a 

 fragment of a penultimate pinna with ultimate pinnae having sterile 

 pinnules from a position still lower than the part shown in Fig. 4. The 

 lobes have here become pinnules. This specimen is distorted from 

 pressure. PL VII, Fig. 6, represents an ultimate pinna magnified two 

 diameters to show the heteromorphous basal pinnules. PL VII, Fig. 7, 

 gives an entire sterile pinnule magnified similarly to show the nerves. 

 PL VII, Fig. 8, gives a dentate sterile pinnule with the same enlarge- 

 ment. PL VII, Fig. 9, gives, with the same enlargement, a fertile entire 

 pinnule to show the sorus. PL VII, Fig. 10, gives, with slightly greater 

 enlargement, a lobed fertile fragment to show the sorus. 



The species occurs most abundanth' at locality No. 2, but is com- 

 mon also at No. 3. It is found also at Nos. 1, 4, 5, 6, 7, 16, and 17. 



DicJxSotiia oregonensis is the most abundant of the Oregon Jurassic 

 ferns and is found at more localities than any of the others. The differ- 

 ent parts show a considerable variation in appearance, as is to be seen 

 in the figures. Before a clo;e comparative study of the different forms 

 had been made I was inclined to think that several species were rep- 

 resented in them. 



