148 [ Senate 



This species resemloles the C. coronata very much, but is smaller, and 

 scarcely ever shows any traces of a sinus on the ventral valve. It is also 

 very near C. nana, with which it has been considered identical : it differs, 

 however, from that species as described by De Verneuil, in having one 

 or two more spines on each side of the beak, and the greater inequality of 

 the areas of the two valves, that of the dorsal or concave valve of our shell 

 being not more than half as broad as that of the ventral valve. The much 

 greater number of striae is also a distinguishing feature. 



Geological position and locality. Hamilton group : Cayuga lake, aiad 

 other localities in Western New-York. 



Chonetes lepida ( n. s.). 

 Shell very small, nearly semicircular ; hinge equalling the 

 greatest breadth, rectangular at the extremities : dorsal valve 

 concave; area linear, leaving a small projecting dental process 

 in the middle : ventral valve convex in the central regions, 

 depressed at the extremities; area rather narrow, arcuate; fo- 

 ramen closed above by a convex deltidium, extending about 

 half way down, occupied below by the prominent dental 

 process of the other valve. Surface ornamented by distinct,, 

 rather strong striee, of which about ten or eleven may be 

 counted near the beaks, but the number is augmented chiefly 

 by intercalation, so that about twenty may be counted round 

 the margin : no concentric striae visible. Two of the striss on 

 each side of the centre near the beak of the ventral valve are 

 larger and more prominent than the others ; the space between 

 them is depressed, and occupied by two or three smaller strise, 

 which are given off from the larger ones on each side. The 

 larger strise are more prominent near the beak than on any other 

 part of the valve, and give almost a bicarinate aspect to the 

 umbo, with a distinct sinus between, which becomes obsolete 

 near the base of the shell. 



This species can be readily distinguished by the small size, the two 

 larger striae and the sinus in the middle. Three or four tubular spines may 

 be counted on each side of the beak, the outer ones of which are nearly 

 vertical to the hinge line. 



Geological position and locality. Hamilton group : Shore of Cayuga 

 Lake. 



