NOTES ON THE FOSSILS OF ONTARIO. 143 



large, three rows occupying the width of the stem, the apertures 

 oval, about four in the space of one line measured longitudinally, and 

 six in the same space measured transversely. The cells are arranged 

 in longitudinal alternating rows, and their apertures are surrounded 

 by thick but not elevated margins. The rows of cells are not separated 

 by elevated lines ; there are certainly no non-celluliferous, striated 

 marginal zones or borders to the frond, and there is no evidence as to 

 the existence of a central laminar axis. It is thus more than 

 doubtful if the species can be referred to Ptilodictya ; but in the ab- 

 sence of any certain knowledge as to its internal structure, its generic 

 affinities must remain uncertain. 



Locality and Formation. — Rare in the Clinton Group at Dundas. 



17. Fenestella tenuis, Hall. {Ref. Pal. N. Y. Vol. II. pi. xix. 

 5a-c.) Fragments of this species are not uncommon in the Clinton 

 group at Dundas, but they are ill-preserved, and their more minvite 

 characters can not be made out. 



18. Ptilodictya punctata, Nicholson and Hinde. Polyzoary 

 forming a thin flattened expansion, or explanate frond, which probably 

 had a circular fcrm when perfect. Cells arranged in sub-alternate rows, 

 separated by elevated thread-like ridges, which are curved in such a 

 manner as to lead to the belief that the rows of cells were concen- 

 trically disposed of round a central point. Mouths of the cells nearly 

 circular, fiom seven to eight in the space of one line measured across 

 the rows, and about five in the same space measured longitudinally 

 or in the direction of the rows. The cells are separated in a longitudinal 

 direction by well marked spaces, which are occupied by from three to 

 six minute rounded pores, the apertures of as many small cells. No 

 such pores are to be detected on the longitudinal ridges which 

 separate the rows of cells, or on the lateral aspects of them. 



Pig. 1. — Ptilodictya {?) punctata, Nich. & Hinde. A, A fragment enlarged ; E, 

 Part of the same still further enlarged. From the Clinton Group. 



The uiternal structure of this singular fossil cannot be made out, 

 and its generic affinities are thus uncertain. Only one side of the 



