84 Forty-fourth Report on the State Museum, 



apertures, and the much more numerous apertures ; in tliat 

 species there are only nine or ten apertures in the space across 

 the branch, while in this species there are from fifteen to twenty ; 

 from P. triquetra and P. subconcava, it is easily distinguished by 

 its much larger branches. 



Formation and locality. — Hamilton group, Hill's gulch, four 

 miles south of LeEoy, N. Y. 



Ptilodictya parallela. 



Ptilodictya parallela, Hall. Palaeontology of New York, vol. vi, p. 270, 



pi. Ixi, figs. 7, 8, 1887. 



When the whole frond is preserved this species is characteristic 

 and will be readily' distinguished ; when occurring only in frag- 

 ments, it sometimes closely resembles Acrogenia prolifera, in 

 some of its aspects, but it may be distinguished by the somewhat 

 larger, less oblique cell, apertures, and the more uniform si«e of 

 the longitudinal ridges ; in that species tHe central ridge is 

 usually much more prominent, frequently having two or three 

 times the width of the others, and they are all often striated. 

 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 

 Ptilodictya 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. angulariSy 

 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, 

 Genesee county, and near the head of Canandaigua lake, Ontario 

 county, N. Y. 



