144 NOTES ON THE FUSSILS OF ONTARIO. 



coencecium is known ; it is therefore uncertain whether both aspects 

 were celluliferous or not. So far as can be judged, the fossil is a 

 Ptilodictya belonging to the same group as P. excellens and P. superha, 

 Billings, in which the ends of the cells are separated by minutely 

 poriferous interspaces — a group which will probably be found to be 

 of at least sub-generic value. It is, however, just possible that the 

 larger openings in the ccenoecium are not the apertures of cells, but 

 actual perforations passing through the whole thickness of the frond, 

 in which case the fossil would be a very aberrant member of the 

 Fenestellidce. There is, however, no direct evidence to support this 

 view ; and but for the porous or punctate intercellular spaces, the 

 fossil has all the characters and appearance of one of the explanate 

 PtilodictycB. 



Locality and Formation. — Clinton Group, Dundas. 



19. Leptoccelia plano-convexa, Hall. {Ref. Atrypa plano- 

 convexa, Pal. N.Y., Vol. II., pi. xxiii., figs. 11a— A.) Abundant in 

 the Clinton Group at Dundas and Hamilton. 



20. Atrypa naviformis, Hall. {Ref. Pal. N.Y., Vol. II., pi, xxiv., 

 figs, lor-k.) Dundas. 



21. Atrypa reticularis, Linn. Dundas. 



22. RHYNCHaNELLA NEGLECTA, Hall. {Ref. Pal. N.Y., Vol. II., 

 pi. xxiii., figs. 4a-/, and pi. Ivii., figs, la-p.) Dundas. 



23. Orthis elegantula, Dalman.— Dundas and Owen Sound. 



24. Orthis calligramma var. Davidsoni, De Vei-neuil. Dundas. 

 2.5. Orthis flabellulum, Sowerby (?). Dundas. 



26. Lept^na sericea, Sowerby. Dundas and Hamilton. 



2.7. Strophomena rhomboidalis, Wahlenberg. Owen Sound. 



28. AvicuLA. ALATA, Hall. {Ref Posidonia{?) alata. Hall. PaL 

 N.Y., Vol. II., pi. xxvii., fig. 4). Dundas. 



29. MoDiOLOPSis ORTHONOTA, Conrad. {Ref Modiolojjsis orthonota. 

 Hall. Pal. N.Y., Vol. II., pi. iv., figs. la-c). Dundas. 



30. Ctenodonta, sp. — Casts of a small but undeterminable 

 Gtenodo7ita are of common occurrence in the earthy hsematite of the 

 Clinton Group at Dundas. 



31. Tentaculites distans, Hall. (Ref Pal. N.Y., Vol. II., pi. xli. 

 A. figs. 9a-c). Tube straight, conical, from six to eight lines in 

 length, and about one line in diameter near the mouth, Annulations 



