284 PALJEONTOLOGY 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. 

 ** * * * * * * * 



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 infreqoens, n. sp. 



PLATE LXVI, FIGS. 26-39. 



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. 



