The branches of this species are very gently convex, while in that
one they are subangular ; but sometimes the resemblance is very
close and from small fragments alone it is difficult to distinguish
the species. From Stictopora subcarinata it is distinguished by
the wider frond, the extremely narrow non-celluliferous marginal
space, the more uniform size of the apertures, and the prominent
ridges separating the ranges of apertures. From other forms of
Ptelodiotta it is distinguished by the circular, comparatively
distant cell apertures; from Stictopora trilineata it is distin-
guished by the circular cell apertures, wider fronds, more
numerous ranges of apertures and the prominent longitudinal
ridges ; from Stictopora rectalinea by the circular apertures and
smooth longitudinal ridges ; from S, subrigida, S. angularis,
S, lineata and S. recta it is distinguished by the much wider
frond, greater number of ranges of apertures, and narrow, promi-
nent, smooth ridges.
Formation and localities. — Hamilton group, Darien Centre,
Q^nesee county, and near the head of Canandaigua lake, Ontario
county, N. T.
Eepobt of the State Geologist. 55

Ftilodictya plumea.
Ptilodictya plumea. Hall. Paleeontoloccy of New York, vol. vi, p. 271, pi. Ixi,

figs. 9-12, mi.
This species most nearly resembles P. retiformis, but may be
distinguished by the more nearly circular, more distant cell aper-
tures, and the convex, granulose, interapertural space ; from
P. scutulata it may be distinguished by the wider frond, the more
d istant cell apertures, and the convex interapertural space ; from
P. faldformis, Nich., P. tenuis, P. nebulosa and P. lirata, it may be
distinguished by the irregular disposition of the cell apertures ;
in those species the apertures being arranged in longitudinal rows.
Formation and locality. — Hamilton group, Hamburg-on-the-
Lake, Erie county, N. T.
Tlxamniscus pauciramus.
