540 MESOZOIC FLORAS OF UNITED STATES. 



their more strongly falcate form. It is not unusual to find pinnules 

 more than 2 cm. long with a width not greater than 5 mm. PL CXIV, 

 Fig. 5, shows a portion of an ultimate pinna with pinnules of average 

 character. In Maryland this fern and the normal form are confined to 

 the Arlington localities. The specimen figured bears the number W. C, 

 B., 5055. 



Cladophlebis alata (Pecopteris strictineevis).* 



In the Lower Potomac flora of Virginia two types of ferns were found 

 and described in Monograph XV as distinct species. They are Clado- 

 phlebis alata and Pecopteris strictinervis. Recently forms have been 

 found in Alaska (see p. 158) that make it probable that these are 

 phases of the same species, for which the name Cladophlebis alata is 

 retained. In the Arlington collections two specimens of the Pecopteris 

 strictinervis type were obtained. The best of these shows a portion of 

 an ultimate pinna with good pinnules. The plant was evidently quite 

 rare here. The specimens are numbered W. C, B., 5045, 5048. 



Drtopteris angustipinnata (Fontaine) Knowlton. 

 PI. CXIV, Fig. 6. 



1889. Aspidium angustipinnatum Font.: Potomac Flora (Monogr. U. S. Geol. Surv., 

 Vol. XV), p. 98, pi. xvi, figs. 1, 3, 3a, 3b, 8, 8a; pi. xvii, figs. 1, la; pi. xix, 

 fig. 10. 



1895. Dryopteris angustipinnata (Font.) K. : Bull. U. S. Geol. Surv., No. 152, p. 91. 



Thirteen specimens of Dryopteris angustipinnata were found among 

 the plants from the Arlington localities. They are not so good as those 

 described in Monograph XV, and no fructified forms were seen. The 

 pinnules of this fern resemble somewhat the narrowest ones of Clado- 

 phlebis acuta angustifolia, but differ from them in important points. 

 The pinnules of Dryopteris angustipinnata are narrower than those of 

 Cladophlebis acuta angustifolia and have nearly the same width from their 

 base to near their apex. They are less falcate and their lateral nerves 

 are less commonly furcate. When forked they do not fork so near the 

 midrib. Very commonly their lateral nerves are simple and parallel. 

 In C. acuta angustifolia the pinnules are much wider at base and they 



"Monograph XV, pp. 77, 78, pi. xix, fig. 5; pp. 84, 85, pi. xiii, figs. 6-8; pi. xix, fig. 9; pi. xx, fig. 3; pi. 

 xxii, fig. 13: pi. clxx, figs. 5, 6. 



