laa PALAEONTOLOGY OF NEW-YORK. 



Chonetes lepida. 



PLATE XXL 

 Chonetu lepida : Hall in Tenth Report on the State Cabinet, p, 148. 1857. 



Shell small, scarcely transverse, semielliptical, subhemisplierical : 

 hinge-line about equalling the width of the shell below. 



Ventral valve more or less gibbous, with a longitudinal depression along 

 the centre in well-marked specimens ; curving abruptly to the front 

 and sides, with cardinal angles scarcely flattened. 



Dorsal valve following the curvature of the opposite valve, with a lesser 

 concavity. 



Area of the ventral valve narrow, distinctly wider in the middle, and 

 sloping with a gentle curve to the cardinal angles. The foramen is 

 small, partially closed by a pseudo-deltidium, and filled by the cardi- 

 nal process of the opposite valve. The dorsal area is scarcely equal to 

 the thickness of the shell. 



Surface marked by slender angular bifurcating strije, of which there 

 are ten or twelve near the umbo and twice as many on the margin, 

 and in some specimens a larger number. Two of the stria), 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 striae, which are given off from the 

 larger ones on each side. The larger striae are more prominent near 

 the beak than on any other part of the valve, and give an almost 

 bicarinate aspect to the umbo, with a distinct sinus which becomes 

 obsolete near the base of the shell. 



The hinge-line usually shows two or three spines on each side of the 

 centre ; but in some individuals, the bases of five spines can be distinctly 

 seen on each side of the beak. 



The interior of the dorsal valve shows a longitudinal depression, and 

 the course of the striae is well defined and strongly papillose. 



The cardinal process has not been seen in its connexion with the 

 dorsal valve. Some casts of the ventral valve show a gibbous centre, 



