24 



Cincinnati Society of Natural History. 



illustrated is smooth. Muscular scars so delicate as not to 

 appear on the casts. In its general outline, it resembles a 

 CypricarditeSy but the absence of muscular scars and the 

 short, highly-inclined cardinal line at once distinguish it. It 

 has some resemblance to the fossil described as Edmondia 

 ventricosa (N. Y. Pal., Vol. I, p. 155), and generally referred 

 to as Cypricardites ventricosus % which is a smaller shell, more 

 prolonged in the postero-basal part, giving it a rhomboidal 

 outline, and is higher in the umbonal region. It is certain 

 that Edmondia ventricosa does not belong to Edttiondia or 

 Cypricardites, and it agrees with this genus in the highly 

 inclined cardinal line, and in showing no muscular scars in 

 the casts. 



This species occurs in the upper part of the Hudson River 

 Group, at Richmond, Indiana. The specimen illustrated is 

 from the collection of C. L. Faber. 



Ambonychia cincinnatiensis, n. sp. 



Plate /, Fig. 8, left valve of an old specimen ; Fig. 9, hinge of 

 the same specimen injured at the distal end of the lateral 

 teeth ; Fig. 10, hinge and lateral teeth of the left valve of a 

 younger and smaller shell. 



Shell below the medium size, and more or less subacutely 

 ovate in outline, varying a little in the extent of the wing 

 bearing the lateral teeth in the different specimens. Posterior 

 side only slightly winged and rounding into the base below. 

 Anterior border of the valves truncated below the beaks, 

 where there is a moderately large byssal opening, and below 

 this the valves very gently round into the base. Base evenly 

 rounded. Umbones low, subangular, below which the valves 

 are depressed convex. Beaks slightly incurved, pointed, 

 terminal and extending beyond the cardinal teeth and hinge 

 line. Surface marked by tolerably fine radiating striae and 

 occasional concentric lines of growth. 



This species has been generally referred to Ambonychia 

 bellistriafa, a New York Trenton form, but there is a wide 

 difference between the two species. A. bellistriata is much 



