638 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.38. 



referred to, Angiopteridium strictinerve , are from Virginia and Califor- 

 nia, while those described as a new species of Sapindopsis, which genus 

 they do not resemble in the remotest degree, are from Oregon. 

 The former are quite different from the type of that species, being 

 smaller and less elongate with closer mostly simple veins and with 

 the rachis prominent below and masked above by the lamina of 

 the frond. The latter correspond with the others in outline and 

 venation, differing in outline, venation, and in the character of the 

 rachis from Sapindopsis. 



The present species, which is confined to the Potomac group and 

 the Shasta of California and Oregon, where it occurs in both the 

 Knoxville and the Horsetown beds, is suggestive of the species 

 from the Neocomien of Japan, which Yokoyama a identifies as 

 Nilsonia johnstrupi Heer. 



Occurrence. — Patuxent formation (?) Chinkapin Hollow, Vir- 

 ginia. — Shasta formation, California (Tehama County, in Knoxville 

 and Horsetown beds), and Oregon (near Kiddles, in Horsetown beds). 



NILSONIA DENSINERVE (Fontaine). 



Platypterigium densinerve Fontaine, Monogr. U. S. Geol. Surv., No. 15, 1890, 

 p. 169, pi. 30, fig. 8; pi. 31, figs. 1, 4; pi. 32, figs. 1, 2; pi. 33, fig. 1; pi. 34, 

 fig. 1; pi. 35, figs. 1, 2. — Fontaine, in Ward, Monogr. U. S. Geol. Surv., 

 No. 48, 1905, p. 521, pi. 112, fig. 8. 



Platypterigium rogersianum Fontaine, Monogr. U. S. Geol. Surv., No. 15, 1890, 

 p. 171, pi. 31, fig. 2; pi. 33, fig. 2; pi. 34, fig. 2. 



Description. — Fronds large, upward of 50 cm. to 70 cm. in length 

 by 15 cm. to 18 cm. in greatest width, averaging about 12 cm., 

 either entire or more often irregularly divided into rectangular or 

 subrhombic segments, at times somewhat rounded proximad. Tex- 

 ture coriaceous. Rachis stout, prominent below, more or less 

 flattened during fossilization. Laterals of small calibre, close, one- 

 third to 1 mm. apart, parallel, invariably simple and nearly straight, 

 diverging at an angle in the neighborhood of 00°. 



This splendid species, presumably because of its large size, is 

 represented only by fragmentary specimens, both the apex and the 

 base being missing. It is not at all common and is entirely con- 

 lined to the Patuxent and Arundel formations in the Maryland- 

 Virginia area. The specimens show some individual variations in 

 the degree of segmentation and strength and position of the Lateral 

 veins, the forms which served as a basis for PlMypterygium roger- 

 sianum, of Fontaine, being more robust, but somewhat smaller than 

 the others, with veins somewhat larger in size and less closely placed, 

 but the limits of variation are nevertheless quite restricted. 



There can be but little doubt of all of these forms belonging to a 

 single species, such variations as are observable being due to varia- 



° Yokoyama, Journ. Imp. Coll. Sci., Japan, vol. 7, 1895, p. 226, pi. 25, figs. 1-4. 



