1908] Chazy Pel?:cypoda 113 



collected by Mr. Sowter, and now in the museum of Yale Univer- 

 sity. At this locality numerous casts of right and left valves 

 have been collected' by Dr. H. M. Ami and by Mr. Sowter. 



In Mr. BiUings' collection of fossils from the Hog's Back 

 there are eleven casts of the interior of single valves of 5. Cana- 

 densis. Most of these are imperfect and badly preserved, the 

 three specimens figured on Plate III being the most perfect but 

 bv no means the largest. In figure 14 on that plate the ventral 

 rnargin is a little restored. The generic definition of Sowteria 

 is largelv based upon these three figured specimens, and the 

 following description of some of their presumably specific 

 characters may be added. Anterior portion of each valve very 

 short, in some specimens truncated almost vertically at its 

 extremitv, in others faintly concave under the leaks above, 

 and rounded at or below the midheight; posterior portion 

 moderatelv elongated, its extremity obliquely subtruncate 

 above and narrowly rounded belov.-. Superior border and 

 ventral margin nearly straight or very gently convex; beaks 

 nearlv or quite terminal. 



In a right valve of 5. Canadensis from Aylmer, collected 

 by Dr. Ami in 1893, there is an oblique, shallow, median de- 

 pression. 



B. From the Chazy shale at the Hog's Back. 

 Ctekodonta parvidens, Raymond. 

 Plate III, fig. 16. 



Ctenodonta parvidens, Raymond. \90S. Amer. Journ. Sci., Fourth 

 Series, Vol. XX, p. 372. 



The cotvpes of this species are two specimens from the 

 Chazv shale at the Hog's Back, collected by Mr. Sowter and 

 now m the museum of Yale University. Both of these specimens 

 show impressions of the hinge teeth. 



C. parvidens appears to be the most abundant and charac- 

 teristic fossil of the Chazy shale at this locality, where specimens 

 have been collected by Dr. Ami and Mr. Sowter, as well as by 

 Mr. Billings. Dr. Ami has also found numerous specimens of 

 it in the Chazy shale at Rockland, on the Ottawa River, twenty- 

 one miles below Ottawa, in the township of Clarence. 



In Mr. BiUings' collection from the Hog's Back there are 

 nine casts of the interior, either of separate valves or of the 

 two valves united, all of which show impressions of at least 

 some of the hinge teeth. The following is an original description 



