15 



few doubtful forms from the Humber member of the Dundas at Port Credit 

 have also been referred provisionally to this species. It is found in the Maysville 

 of Ohio and the Pulaski of New York. 



Modiolopsis concentrica, Hall and Whitfield. — This is a common species 

 throughout the Cincinnatian series of Ontario, but in Ohio it is found only in 

 the Richmond. On the Credit river it is found in both members of the Dundas 

 formation and in all three members of the fossiliferous Richmond. 



Modiolopsis postplicata, Foerste. — A single example of this species was 

 found in the Humber member in the quarry at Port Credit. It has previously 

 been reported from the Pulaski of Quebec, Dundas of the Humber river, and 

 doubtfully from the Waynesville of Quebec. 



Modiolopsis versaillensis, Miller. — A single example of this species is among 

 the older collections of Streetsville fossils in the Royal Ontario Museum of 

 Paleontology. The exact stratigraphical horizon from which it came is not 

 known. 



Modiolopsis borealis, Foerste. — A single right valve of this species was found 

 in the Credit member on the Credit river, just below Erindale. Foerste reports 

 the same species from the Lorraine, one mile south of the clay cliffs, at the 

 eastern end of Manitoulin island. 



Opisthoptera fissicosta, Meek. — The range of this species is higher in the 

 Credit River section than in the Ohio valley. In Ohio it occurs in the Waynes- 

 ville, but on the Credit it is found in the Streetsville and Meadowvale members 

 of the Richmond. It has not yet been obtained from the Erindale. 



Orthodesma cf. canaliculatum, Ulrich. — A pelecypod was found in the 

 Streetsville member which in outline, in the character of the concentric striae, 

 and in the prominence of the anterior and posterior muscle scars, is close to 

 Orthodesma canaliculatum of the Blanchester division of the Waynesville of 

 Ohio. The peculiar pallial line and radiating striae seen in the type are not 

 present on the Credit River specimens. 



Ortonella cf. hainesi (Miller). — One specimen of a pelecypod was found in 

 association with Ischyrodonta miseneri in the Streetsville member, which greatly 

 resembles the above species in outline and in the character of the concentric 

 plications. The preservation of the specimen, however, is too imperfect to 

 allow any indication of the lunule and escutcheon characteristic of 0. hainesi 

 to be seen, and hence it can only be placed provisionally under that species. 



Pterinea demissa, Conrad. — This species is abundant and evenly distributed 

 throughout all the divisions of the Cincinnatian series of the Credit River section. 



Whiteavesia pholadiformis (Hall). — Fragments of the shells of this species 

 showing the characteristic transverse plications are found in all the divisions 

 of the Dundas and Richmond formations of the Credit River section with the 

 exception of the Queenston. No complete specimens, however, were found. 

 W. pholadiformis is a characteristic Richmond species in the Ohio valley, but 

 has not been found in the Maysville or Eden of that area. In Ontario, on the 

 other hand, it has been found in all the divisions of the Cincinnatian series with 

 the exception of the Utica. 



Whitella cf. hindi, Billings. — A few examples of a pelecypod, very similar 

 in form to this species were found in both the Credit and Humber members of 



