101 



subpeltate, and therefore they should be referable to Pterospermites. The anal- 

 ogy of some of these leaves to those of the living Ptcrospermum acerifolium, 

 "Wild., is indeed evident. In this, however, the essential nerves, thi-ee or five, 

 end into the point of a lobe, while all their branches and the intermediate 

 nerves are camptodrome. And though the base of the leaves is overlapping 

 and covering, by its broad auricules, the upper part of the petioles, all the 

 lower veins come out from the top of the petiole, and there is no trace of the 

 horizontal vinelets, which are remarked, without exception, in all the species 

 which I describe in this new genus. I do not know of any leaves of Ptet 

 ospermites but those which are described by Heer from Greenland. In 

 PL Arct., (p. 480, PL xliii, Fig. 15 b , PL liii, Figs. 1-4, and PL liv, Fig. 3,) 

 the author has described two species, Pterospermites spectabilis and P. alter- 

 nans, whose nervation and cordate base are of the same character as in the 

 species of Credneria, the only difference being in the size of these leaves, 

 which appear smaller. Of these fragments, Fig. 15 b is comparable, by its 

 basilar nervation, to the Cretaceous leaf of this memoir, (PL xvii, Fig. 3,) 

 which, however, differs from the Greenland species by its craspedodrome 

 nervation. In the same work, Heer has (p. 122, PL ix, Fig. 14a) Pteros- 

 permites integrifolius without any horizontal basilar nerves, the medial nerve 

 passing under the border-base of the leaf or peltate, and (p. 138, PL xxi, Fig. 

 17 b , and PL xxiii, Figs. 6, 7,) he represents Pterospermites dentatus with a 

 peltate leaf and basilar veins running down from the base of the medial 

 nerve, or with secondary veins at right angle to it. It is, therefore, difficult 

 to know by what characters the genus Credneria may be positively separated 

 from Pterospermites, besides that of larger-sized leaves for the former genus, 

 and of more or less peltate ones for the second. Some of our peltate leaves, 

 however, referable to Pterospermites by the nervation, have leaves, as re- 

 marked already, as large as those of Credneria. Having, therefore, to 

 describe a number of forms which, though related to the yet undefined 

 genera Credneria and Pterospermites, are forcibly removed from them by 

 some important characters, I have united them all in this new division. 



Pkotophyllum sternijeegii, Lesqx., PL xvi ; PL xviii, Fig. 2. 



Leaves large, coriaceous, entire, round or cordate at the base, narrowed upward into a slightly obtuse 

 point ; basilar nerves one or two pairs. 



Pterospermites sternbergii, Lesqx., Hayden's Report, 1872, p. 425. 



PL xvi represents a splendid leaf, of which only one-half is preserved. 



