Raymond : The Chazv Formation and its Fauna. 577 



Locality. — A very rare fossil in the Chazy at Crown Toint, New 

 York. 



Gyroncma ? rotalinca sp. nov. 



Shell of good size for this genus, with about five whorls and an acute 

 spire. The whorls expand gradually below, the body whorl occupy- 

 ing about half the length or a little less. All the whorls are robust, 

 nearly circular in section. The sutures are deep. The first three 

 whorls are smooth, but the last two show four or five revolving ridges 

 on the lower side of the whorl, the upper half being smooth. The 

 height is i8 millimeters; the width of the last whorl 14 millimeters. 

 The aperture is large and rounded. The umbilicus is not shown by 

 the present specimens. 



Locality. — Found in the middle division of the Chazy at Valcour 

 Island, New York. 



Holopea ? plaiita sp. nov. 



Shell small, depressed. Spire scarcely elevated above the level of 

 the body whorl. There are usually two and a half or three volutions, 

 the body whorl expanding very rapidly. Along the outside and at 

 about the middle of the main whorl is a slight ridge, and below this 

 revolving ridge are a series of low, broad folds running back into the 

 umbilicus. \Yith this exception the surface is smooth. The aperture 

 is rounded below and rather acute above. The umbilicus is very wide. 



Locality. — A rare shell found in division 2 at Yalcour Island, and 

 in zone 3a at Chazy, New York. 



Pelecypoda. 



Ctenodonta ? bidorsata sp. nov. 



Shell small, longer than high. Hinge back of beak nearly straight, 

 rather long. Anterior end of shell short and broadly rounded. The 

 lower margin is gently convex, and the posterior margin short and 

 acute. The interior cast is marked by two narrow sinuses which 

 radiate from the beak. The anterior one runs almost directly across 

 the height of the valve, while the posterior one runs diagonally to the 

 posterior margin. In front of the anterior sinus, and behind the pos- 

 terior one are narrow ridges. The casts are only slightly convex, 

 highest at the umbo, and concave along the hinge margin. .An 

 average specimen is 11 millimeters long and 7 millimeters high. 



