CLADOPHLEBIS. 93 



frigida, Heer, the pinnules of which are longer, stiff er, and less 

 falcate. 1 



Fontaine does not include Cladophlebis Albertsii (Dunk.) among 

 the Potomac plants, but some of the pinnae which he figures 

 strongly resemble this species. As in the case of Thyrsopteris, there 

 appear to be some exceedingly narrow and ill-defined differences 

 between certain species. In sterile fronds of a type similar to 

 those of C. Albertsii it is hardly possible to determine the specific 

 limitations with any certainty; possibly no form of frond is so 

 widely distributed in Jurassic and Lower Cretaceous rocks in all 

 parts of the world. 



C. virginiensis, Font., 2 possesses pinnules a trifle broader and 

 shorter than those of C. Albertsii, and with entire margins. In 

 C. denticulata, Font., 3 there is a very distinct resemblance to C. 

 Albertsii, but the fragments on which the species is founded are 

 too small to enable us to form an opinion as to the frond as a 

 whole. 



C. falcata, Font., 4 is another fern of very similar form, but it 

 suggests a larger frond than that of C. Albertsii and differs in the 

 lobed margins of some pinnules; it is difficult to separate some 

 of the figures of C. virginiensis, Font., from those of C. falcata, 

 Font. In describing the former species Fontaine remarks that 

 "The Potomac plant is strikingly like Brongniart's Pecopteris 

 Whitbiensis and P. tennis, and one may well hesitate to separate 

 them." 5 There is also the following remark with reference to the 

 same species which might be applied, in principle, to other ferns 

 from the Potomac beds: "It does not, however, seem proper to 

 make the Potomac plant an Asplenium so long as it shows no 

 fructification." Another species, C. acuta, Font., 6 has the same 

 type of frond as C. Albertsii and other ferns ; it is spoken of as 

 " more like Dunker's Neuropteris Albertsii .... than any other 

 previously described fossil, and is no doubt quite near the Wealden 

 species." The same species is compared also to Heer's Pteris 

 Albertsii and Schenk's Alethopteris Albertsii. The resemblance 



Abh. k. bohm. Ges. Wiss. math.-nat. 01. vol. ii. Folg. 7, 1888. 



Potomac Flora, p. 70, pi. iii. figs. 3-8 ; pi. iv. figs. 1 and 3-6. 



Ibid. p. 71, pi. iv. fig. 2 ; pi. vii. fig. 7. 



Ibid. p. 72, pi. iv. fig. 8 ; pi. v. figs. 1-6, etc. 



Ibid. p. 71. 



Ibid. p. 74, pi. v. fig. 7 ; pi. vii. fig. 6, etc. 



