46 
cated by their consistency and substance, and that they are not shrivelled 
fruits is suggested by the regularity of the elevated bosses and intervening 
depressions. 
The genus Stenorachis to which they are referred was proposed by 
Saporta in 1875 for late Triassic and early Jurassic forms which Nathorst 
had referred to Zamiostrobus, and was considered by Saporta, a view in 
which Nathorst subsequently concurred, as the fruiting parts of some 
Ginkgoalean plant. Seward subsequently proposed to transfer to Steno- 
rachis several forms of supposed staminate sporophylls which Heer had 
described and referred directly to Ginkgo, which it must be admitted they 
much resemble. There is absolutely no definite proof of the morpho- 
logical nature of Stenorachis, or whether the lateral appendages are axillar 
or foliar in nature, indeed it seems very probable that the genus is really 
a composite, since sometimes these appendages are simple, as in the present 
case; at other times they are forked; sometimes they suggest staminate 
sporophylls, and sometimes they suggest seed-bearing sporophylls. The 
type of the genus, Stenorachis scanicus (Nathorst) Saporta, has the appear- 
ance of the Ginkgoales, but as mentioned above, this Canadian material 
may be Filicalean. Similar objects are not uncommon during the Jur- 
assic, but I do not recall any from as recent a horizon as the Lower Blair- 
more. 
Genus, nilsonia Brongniart 
Nilsonia densinerve (Fontaine) Berry 
Platypterigium densinerve Fontaine, XJ.S. Geol. Surv., Mon. 15, p. 169, PI. 
30, fig. 8; PI. 31, figs. 1-4; PI. 32, figs, 1, 2; PL 33, fig. 1; Pl. 34, fig. 
1; PL 35, figs. 1, 2 (1890); Idem., Mon, 48, p. 521, PL 112, fig, 8 (1906). 
Platypterigium rogersianum Fontaine, U.S. Geol. Surv., Mon. 15, p. 171, 
Pl. 31, fig. 2; Pl. 33, fig. 2; PL 34, fig. 2 (1890). 
Nilsonia densinerve Berry, Lower Cretaceous, p. 362, Pis. 57, 58 (1911). 
Fronds large, upwards of 50 to 70 cms. in length by 15 to 18 cms. in 
maximum width, averaging about 12 cms. normally, either entire or more 
often irregularly divided into rectangular or sub-rhombic segments, which 
are at times somewhat rounded basally. Texture coriaceous. Bachis 
stout, prominent on the under side of the frond. Laterals of small calibre 
relatively, closely spaced simple, nearly straight and parallel. 
This species was described originally from material that came from the 
older Potomac of the Atlantic Coastal Plain (Patuxent and Arundel 
formations) to which it is confined with the exception that two specimens 
from the Lower Blairmore locality CH4 appear to represent it. These are 
small fragments of entire fronds about 5 cms. wide. They are hence 
slightly smaller than is normal for this species and have a correspondingly 
more slender rachis, but are otherwise similar. Since it is to be expected 
that small as well as large fronds were necessarily present in this species, 
and no other described form of Nilsonia is comparable, I have considered 
that these two specimens from locality CH4 represent it in the Lower 
Blairmore. 
