14 



original description of B. richmondensis , Ulrich states that although the ribs 

 are difficult to count, there are not less than 50 of them on each valve. Foerste 

 also states that the valves of B. robusta are relatively shorter and broader than 

 those of B. richmondensis. It is Foerste's opinion, however, that these two forms 

 are very closely allied if not identical, B. richmondensis being a laterally com- 

 pressed form of B. robusta. 



Byssonychia cf. praecursa, Ulrich. — Pelecypods resembling B. radiata, 

 but with the flattening of the anterior side characteristic of B. praecursa, are 

 found in the Strophomena varsensis zone in the Erindale member of the Richmond 

 and in the Credit member of the Dundas formation on the Credit river. Typical 

 forms are found in the Pulaski shale of New York and in the Maysville of Ohio. 



Clidophorus fabula (Hall). — This species is found in the shale overlying the 

 Columnaria reef in the Meadowvale member of the Richmond. In Ohio, it 

 ranges from the Eden to the Richmond. 



Clidophorus planulatus (Conrad). — This is a common species in the Eden 

 and Maysville of Ohio and the Pulaski shale of New York, but in Canada it 

 extends its range upward into the Richmond. It has been reported from the 

 Waynesville of eastern Ontario and Quebec. On the Credit river, one example 

 was found in the Credit member of the Dundas formation and one in the Erindale 

 member of the Richmond. 



Ctenodonta cingulata (Ulrich). — A single well-preserved example of this 

 species was found in the Strophomena varsensis zone. C. cingulatu occurs in 

 the Richmond in Ohio, Kentucky, and on Manitoulin island, but one example 

 from the Dundas formation of the Humber river has been referred to it by Miss 

 H. Stewart. 



Ctenodonta filistriata, Ulrich. — Two or three examples of this species were 

 found in the Humber member on the Credit. It is found all through the Dundas 

 formation of Toronto with the exception of the Credit member. In the United 

 States it is found only in the Eden of Kentucky. 



Cuneamya scapha brevior, Foerste. — This form occurs abundantly in shale 

 of the Humber member in the quarry at Port Credit. In the State of New 

 York and the Province of Quebec, it is found in the Lower Lorraine shales, and 

 in the vicinity of Toronto it is found both on the Don and on the Humber river. 



Cymatonota cf. lenior, Foerste. — Fragments of the shells of a species of 

 pelecypod evidently referable to C. lenior were found in the Credit member of 

 the Dundas formation. Previously C. lenior had been reported by Foerste 

 from rocks in Quebec which he correlates with the Pulaski and by Stewart 

 from the Dundas formation of the Humber river. 



Ischyrodonta miseneri, Ulrich. — Well preserved examples of this species 

 were found on the Credit river, in the lower five feet of the Streetsville member, 

 herein called the zone of /. miseneri. The Streetsville specimens are a little 

 thinner than the type forms from Indiana, but in all other respects they are very 

 similar. In Indiana and Ohio, according to Shideler, /. miseneri is found in the 

 Upper Whitewater. 



Ischyrodonta unionoides (Meek). — One beautifully preserved and unmis- 

 takable example was found in the Credit member of the Dundas formation. A 



