ADDITIONS TO THE FLORA OF THE WILCOX GROUP. 



the Paleocene of Franco, which has the dis- 

 tinction of having the receptacles preserved 

 and therefore being conclusively identified. 

 The present form is also much like MarcTiantia 

 jxuli i Knowlton, 4 of the Fort Union formation 

 of Montana. 



Thalloid liverworts are so rarely found in 

 the geologic record that any qf them arc note- 

 worthy. Similar remains are recorded from 

 several Jurassic and Lower Cretaceous out- 

 crops both in this country and abroad, and 

 several Eocene and Oligocene species have 

 been described. 



The present species is named for the col- 

 lector and comes from the upper Wilcox de- 

 posits near Jacksonville, Pulaski County, Ark. 



Phylum PTERIDOPHYTA. 



Class LEPTOSPOKANGIATAE. 



Order POLYPODIALES. 



Family POLYPODIACEAE 



Genus DRYOPTERIS Adamson. 



Dryopteris cladophleboides Knowlton. 



Plate IV, figures 5-7. 



Dryopteris? cladophleboides Knowlton, U. S. Geol. Survey 

 Prof. Paper 101, p. 284, pi. 54, fig. 1, l!lls. 



Frond pinnate or bipinnate. Pinnae long, 

 linear-lanceolate, divided nearly or quite to 

 the rachis into numerous ovate-lanceolate, 

 oblong, or conical obtuse or acutely pointed 

 pinnules, with entire margins. Texture coria- 

 ceous. Rachis stout, channeled. Midrib of 

 pinnules stout, diverging from the rachis at 

 angles of about 65° to 70°, curving slightly 

 upward distad, its course throughout nearer to 

 the proximal margin of the pinnule. The 

 lateral veins are thin and closely spaced; they 

 diverge at wide angles and number about 16 

 pairs. Those in the tip of the pinnule are 

 simple; the majority are once forked; several 

 basal pairs, particularly on the proximal side 

 of the pinna, pass from a single lateral with 

 two simple branches to a lateral with two 

 dichotomous forks, as shown in the accom- 

 panying figure. There is some variation in the 

 shape and degree of separation of the pinnules. 



The specimens are five in number, and none 

 are especially complete. All are sterile. The 

 pinnae were at least 10 centimeters in length, 



* Knowlton, F. H., U. S. Nat. Mus. Proc., vol. 3.5, pp. 157-159, pi. 25, 

 1908. 



and the pinnules are about 1 centimeter in 

 length by about 4 millimeters in width at their 

 base. There is in the collection, however, a 

 tiny specimen showing about 5 millimeters of 

 a similar rachis with the impression of four 

 stout pinnules. These are slightly smaller 

 than the sterile pinnules but have the same 

 form and confluent bases; the midribs are 

 stout; the lateral veins are thin and fewer than 

 in the sterile pinnules; about halfway between 

 the midrib and the margin each lateral shows 

 the impression of a small, approximately circu- 

 lar and prominent sorus, and these decrease in 

 siae distad; there are about six prominent 

 ones in each half of the lamina. Several of the 

 proximal laterals are seen to be forked beyond 

 the sori, but the majority appear to be simple. 



Although these fertile pinnules are not in 

 organic union with the sterile parts of the 

 frond, their association in a thin stratum at the 

 same outcrop and the further fact that no simi- 

 lar species are known in the whole Wilcox flora 

 make it seem very probable that both belong 

 to the same form, and this conclusion is cor- 

 roborated by their form and attitude, similar 

 rachis, similar midrib, and lateral veins. 



The type material of this species, described 

 by Knowlton. came from the Raton formation 

 of southeastern Colorado. It was very incom- 

 plete, with the venation obscured. There 

 seems to be no doubt, however, that the Wilcox 

 occurrence represents the same species, a type 

 of fern hitherto unknown in the Wilcox flora, in 

 which ferns are unusually scarce. 



Both the sterile and fertile pinnules are simi- 

 lar to those of certain species of AlsopJiila and 

 Cj/a/hea, and the}- are practically identical with 

 a number of existing species of Dryopteris, as 

 for example Dryopteris concinnum Mettenius, 

 D. rnolle Swartz, and D. pteroides Swartz. I 

 can see no reason for questioning their reference 

 to Dryopteris. 



The genus Dryopteris is a large one m the 

 modern flora, with more than 1,000 species 

 variously segregated or aggregated by students 

 of existing ferns in the genera Lastrea, Nephro- 

 iliiim, Phegopteris, Polyhotrya, and Dryopteris. 

 Christensen 5 unites them all in a single genus 

 divided into 10 subgenera, many of which are 

 entitled to generic rank, as I have pointed out 

 several times in describing Tertiary species of 



6 Christensen, C, On a natural classification of the species of Dryopteris: 

 Saertryk af Biologiske ArbeijdnerTilegnedeE. Warming, pp. 73-85, 1911. 



