no.1769. FOSSIL I'LAXTS OF I III: POTOMAC CROUP BERRY. 637 



The genus Nilsonia appears in the Triassic and is particularly a 

 Kinetic and Oolitic type. A number of undoubted species occur, 

 however, in the Lower Cretaceous, no less than seven different species 

 having been recorded from the Lakota, Kootenai, and Shasta deposits. 

 The Neocomien of Japan furnishes two or three species, while the 

 widespread Nilsonia schaumburgensis (Dunker) Nathorst, occurs very 

 abundantly at a number of European Wealden localities. The Upper 

 Cretaceous shows a species in the Atane beds of Greenland and one 

 in the Cenomanien of Bohemia, while several supposed species have 

 been recorded from Tertiary strata. 



There are two species in the Potomac group, a lanceolate unseg- 

 mented form variously described by Fontaine as Angiopteridiurn and 

 Sapindopsis and the large and elegant form which this author 

 describes as two species of Platy pterygium. The latter term was pro- 

 posed by Schimper in 1880 as a subgenus of Anomozamites for very 

 large forms of that type. It was subsequently used as a genus by 

 Feistmantel and Fontaine although this usage seems unwarranted, 

 especially since the Platy pterygium forms of Anomozamites are all 

 confined to much older horizons and the Potomac forms agree in all 

 essential characters with Nilsonia, a, relationship suggested by Seward 

 in 1900 after examining the material in the U. S. National Museum. 

 As illustrated by Fontaine the rachis is represented as very wide and 

 the opposite segments are far apart. That the midrib was not wide 

 and flat in life, but prominent below and not out of proportion to the 

 size of the fronds is shown by a most casual examination of the con- 

 siderably macerated and much flattened specimens. 



NILSONIA OREGONENSIS (Fontaine). 



Angiopteridiurn strictinerve Fontaine, Monogr. U. S. Geol. Surv., No. 48, 1905, 

 I.)). 240, 511, pi. 66, figs. 5-7; pi. 110, fig. 12 (not Fontaine, 1890). 



Sapindopsis oregonensis Fontaine, Monogr. U. S. Geol. Surv., No. 48, 1905, 

 p. 268, pi. '69, figs. 1.5-17. 



Description. — Frond simple, unsegmented in all the specimens 

 collected, lanceolate in outline, with equally pointed apex and base. 

 Length apparently about 7 cm. to 15 cm. and greatest width, which 

 is midway between the apex and the base, 1 .2 cm. to 1 .6 cm. Texture 

 coriaceous. Rachis stout, prominent below. Lateral veins close 

 and parallel, the great majority simple, but an occasional vein 

 forking dicliotomously. Angle of divergence large, varying from 

 55° in the apical part of the frond to 85° in I he median and basal 

 portions. 



This species is based upon considerable incomplete material from 

 widely separated localities, which afforded the basis for two different 

 species of Fontaine, but which seem to be identical and markedly 

 different from the types to which they were referred. The forms 



