338 Annals of the Carnegie Museum. 



This is one of the commoner species of the Middle Chazy. All the 

 specimens are casts of the exterior. The change in generic reference 

 is due to Mr. Ulrich, who has seen some of the typical specimens. 



Description. 



Shell roughly rectangular in outline, strongly convex at the umbo 

 and along a ridge which runs diagonally across the shell to the lower 

 posterior angle. In front of this ridge there is usually a slight depres- 

 sion running from the umbo to the middle of the lower margin. The 

 posterior margin is regularly rounded, and the basal margin straight 

 or slightly concave. 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 

 than that to the hinge. The surface is marked by fine concentric 

 lines. 



Locality. — Rather common in the middle Chazy at Valcour Island, 

 New York. 



Genus Modiolopsis Hall. 



i6. Modiolopsis fabaformis Raymond. (Plate XXX, figures 12, 13.) 

 Modiolopsis fabaformis Raymond, American Journal of Science (Ser. 4), Vol. XX, 

 190S. P- 374- 

 This little shell, which much resembles the Modiolopsis faba of the 

 Trenton, is the one pelecypod which is common in the upper layers 

 of the Chazy at Valcour Island. In the upper one hundred feet of 

 the section at that point it is quite abundant in connection with 

 CamarotcBchia plena. It is related only to Modiolopsis exanimis of 

 the Chazy species of the genus. 



Description. 



Shell small, narrow, thick, with a strong ridge extending from the 

 umbo to the lower posterior angle. In front of this ridge is a deep 

 depression which continues to the middle of the ventral margin, making 

 that margin sinuate. The anterior ear is small and convex; anterior 

 margin narrowly rounded. Posterior margin broadly rounded, not 

 oblique as in Modiolopsis parviuscida. The surface is marked by 

 numerous lines of growth. This is not the Modiolopsis fabceformis 

 of Whiteaves,^^ which is a shorter and higher shell. 



Locality. — Common in the Upper Chazy on Valcour Island, New 

 York. 



22 Ottawa Naturalist, Vol. XXII, 1908, p. no, pi. Ill, figs. 7-9. 



