372 P. E. Raymond — Fauna of the Chazy Limestone. 



longer than the posterior, which is regularly rounded. Front 

 margin rather acute. All the specimens are of casts without 

 trace of hinge teeth, muscle scars, or surface markings. 



Largest specimen : Length 19 mm ; height 10*5 mm . Another : 

 Length 17 mm ; height 9 mn C 



Locality.— -Sloop Bay, Valcour Island. The type is in the 

 Yale University Museum. 



Ctenodonta parvidens sp. nov. 



Shell oval in outline, usually flattened, but specimens from 

 the harder layers show considerable convexity below the umbo, 

 with regular slopes to the anterior, posterior, and ventral mar- 

 gins. The cast shows the impression of numerous very tine 

 teeth on the hinge, but the number can not be counted as the 

 beak is always flattened down upon the impression of the 

 hinge. One specimen exhibits 5 teeth on the anterior portion 

 of the hinge. Another shows 7. The surface is marked by 

 very numerous fine concentric lines of growth. 



Locality. — In shales and limy clays at the Hog's Back, 

 Ottawa. 



Glidophorus obscurus sp. nov. 



Shell small, longer than high, not very convex. Basal mar- 

 gin nearly straight, anterior margin regularly curved, posterior 

 end compressed, the margin acutely rounded. In front of the 

 beak the cast shows a short clavicular impression, which 

 extends about half the distance to the lower margin. 



Length 6 mm ; height 4 mm . 



Locality. — Trilobite layers, Sloop Bay, Yalcour Island. The 

 type is in the Yale collection. 



Cyrtodonta tranceps sp. nov. 



Shell roughly rectangular in outline, strongly convex at the 

 umbo and along a ridge which runs diagonally across the shell 

 to the lower side of the posterior margin. In front of this 

 ridge there is usually a slight depression running from the 

 umbo to the middle of the lower side. The posterior margin 

 is regularly rounded, the lower side straight or slightly 

 indented. The anterior end extends a short distance in front 

 of the beak. The slope to the hinge is flat and rather steep. 

 The slope to the front and base is gently convex and more 

 gradual. The surface is marked by numerous concentric lines. 



Locality. — Yalcour Island, New York. The type is in the 

 collection of the Carnegie Museum. 



