OF DENISON UNIVERSITY. 
155 
of the fenestrules being frequently more or less acute. The compara- 
tive width of branches and enclosed fenestrules has no specific 
value whatever, the character of real importance being the form of the 
cells, which are elongated oval in form, the length equalling about 
twice the width. The cell apertures are arranged between quite prom- 
inent longitudinal ridges. From 6 to 7 cells occupy a length of 2 mm. 
The base of the only frond preserving this feature seems to pass with- 
out interruption into a stipe about 4 mm. broad and 18 mm. long, to- 
wards its origin the base becomes rapidly attenuated and may have ar- 
ticulated with some expanded, rooting structure. Until more speci- 
mens of this kind are discovered, this feature can have no value. 
Locality and position. Soldiers’ Home Quarries, very common at 
Fair Haven, Clinton Group. 
Genus PTILODICTYA, Lonsdale. 
Zoaria wedge-shaped below, above expanding into an undivided 
leaf-like expansion. The cells are arranged in diagonal cross-rows or 
have a plumose arrangement, diverging in rows from central longitudi- 
nal series of cells, which usually are of smaller size. Interstitial cells 
wanting. A non-poriferous margin occurs in most species, this if 
present in the following species must be very narrow. 
V. Ptilodictya expansa. Hall and Whitfield. 
{Plate XV, Fig. 5; Plate XVI I, Fig. 5.) 
Phaenopora (Ptilodictya) expansa, Hall and Whitfield, 1875; Ohio, Pal. 
Vol. II. Plate V. fig. I, is a specimen of Phcenopora platyphylla., 
James, 1879. 
Ptilodictya expansa, Hall, 1883 ; 12th Indiana Geol. Rep. The original de- 
scription is here republished, but Plate 12, figs. 2 and 3 are correctly identified. 
Frond arising from a wedge-shaped base, gradually enlarging, 
forming lanceolate expan.sions, or elongated oblong forms with paral- 
lel sides. Epithecal membrane marked by lunate lines of growth 
along the mesial series of cells, their convex sides directed forward ; 
along the sides of broad specimens there are often longitudinal wrin- 
kles, perhaps indicating that these specimens were derived from the 
narrower forms by lateral growth. Along the middle of the frond ex- 
tend from 4 to 7 longitudinal series of cells, which are always con- 
