284 
PALAEONTOLOGY OF NEW YORK. 
on each branch; on the midrib they are alternating, the smaller ones very 
fine, scarcely perceptible. Dissepiments very slender, width less than half 
that of the branches, rounded, finely striated, depressed below the plane of 
the branches and scarcely expanded at their junction, usually distant about 
1 mm., but sometimes two occur very close together, not more than .20 mm. 
distant. On the celluliferous face the mibrib is of about the same convexity 
as on the opposite side; the lateral branches are more abruptly convex, the 
midrib striated, striations similar to those of the opposite face. Cell aper¬ 
tures in two ranges, those on the midrib oval, opening laterally, so that look¬ 
ing directly upon the surface they can scarcely be distinguished; separated 
by less than the length of an aperture, fourteen in the space of 5 mm. 
Lateral branches very much depressed ; apertures a little larger, more nearly 
circular and more conspicuous than on the midrib, opening laterally, sepa¬ 
rated by about two-thirds the diameter of an aperture; when occurring 
opposite a dissepiment they frequently extend a short distance upon it and 
open directly outward. Peristomes of all the apertures thin, distinctly and 
equally elevated. Dissepiments abruptly rounded and very much depressed. 
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Formation and localities. Hamilton group, Moscow, Livingston county, and 
other localities in Central and Western New York; and also at West Williams, 
Ontario, Canada. 
Ptilopora infrequens, n. sp. 
PLATE LXVI, FIGS. 26-29. 
Midrib slender, width, on the fragments observed, about .33 mm., scarcely 
tapering; branches one-half the width of the midrib, distant about 1.25 mm.; 
midrib and branches striated, striae alternating in size. Dissepiments very 
slender, much depressed below the plane of the branches, and not expanding 
at their junction. The celluliferous face has not been observed. 
This species will be easily distinguished from Ptilopora striata and P. nodosa 
by the much less frequent lateral branches. 
