540 MESOZOIC FLORAS OF UMTED STATES. 



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

 more than 2 cm. !on<r with a width not greater than .5 mm. PI. CXIV, 

 Fig. "). shows a |)oiti()n 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., oOoo. 



Cladophlebis .\lata (Pecopteris strictinervis)." 



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

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

 jihlehis (data and Pecopteris striciinervis. Recently forms have Ijeen 

 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 

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

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

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



Dryopteris angustipinnata (Fontaine) Knowltnn. 

 PI. CXIV, FiR. 6. 



1889. Aspidium angustifinnatum Font.: Potomac Flora (Monogr. U. S. Geo). Siirv., 

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

 fig. 10. 



1895. Dryopteris angustipimiata (Font.) K.: Ball. U. S. Geol. Siirv., No. 152, p. 91. 



Thirteen specimens of Dryopteris angustipinnata were foiuid 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 

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

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

 The pinnules of Dryopteris angustipirrnata 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. .xi.x, fig. 5; pp. 84, 8.5, pi. xiii, figs. 6-S; ])]. xix, lig. !); pi. .xx, lig. 3; pi. 

 xxii, fig. 1.3: pi. clxx, figs. .5, 6. 



