272 PALAEONTOLOGY OF NEW YORK. 



Ptilodictya retiformis, n. sp. 



PLATE LXI, FIG. 13. 



This species, in its manner of growth and general appearance, is very similar 

 to P. plumea, but the cell apertures are more nearly oval, and more closely dis- 

 posed. The interapertural space is angular, minutely granulose, and with a 

 prominent node at each cell angle. The surface is not marked by maculae or 

 monticules. It may be distinguished from P. scutulata, which it closely resem- 

 bles in its surface characters, by its much wider frond. 



Formation and locality. Hamilton group, Alden, Erie county, N. Y. 



Ptilodictya scutulata. 



NOT KiaURBD. 



iStictoporaf scutulata, Hall. Ti-ans. Albany Institute, vol. x, p. 191. 1881. 

 " " " Report of State Geolo^st for 1883, p. 47. 1884. 



ZoARiUM consisting of a flattened frond, width from 1.50 to 2.50 mm.; without 

 non-celluliferous marginal space. Transverse section lenticular, greatest 

 thickness .25 mm. ; marginal angles not acute. Cells tubular, arising from a 

 mesotheca. Cell apertures oval, length .20 mm., width two-thirds the length, 

 closely disposed, nearly in contact, sometimes irregularly disposed, at other 

 times forming oblique intersecting rows. The interapertural space is elevated, 

 angulated, having a line of minute nodes or granules, and frequently 

 more prominent nodes at the angles. The surface presents a reticulated 

 appearance. 



Since no bifurcations have been observed, and as specimens more than 20 

 mm. in length occur without branches, it seems sufficient evidence to remove 

 it from Stictopora to which it was originally referred. The cell apertures 

 resemble those of Ptilodictya retiformis, but the species may be distinguished 

 by its much narrower form. It has precisely the appearance of a flattened 

 frond of some specie, of Orthopora, but the mesotheca and manner of growth 

 of the cell tubes show its alliance with Ptilodictya. 



Formation and locality. Hamilton group, near the head of Canandaigua lake, 

 Ontario county, N. Y. 



