No. 109.] 119 



eating and increasing by interstitial addition, so that the margin 



of the shell presents from sixty to seventy (or perhaps a greater 



number in large specimens) : striae distinct, rounded, and the 



depressions between them sharply defined j area narrow, linear. 



Interior striate papillose. 



The striai extend over the entire surface of the shell, and are 



as distinct on the laterocardinal extremities as elsewhere upon 



the surface. 



This species is about the same size and general form as the Choneies 

 pusilla ; but the striaj are much finer, and, when no exfoliation has taken 

 place, are well defined, extending to the cardino-lateral margins, while in 

 that species a considerable space at the angles is plain. It is a sm:i]lor and 

 more rotund species than ChoneUs scitida ; resembling C. glabra in form 

 and proportions, but difi"ering in the character and distribution of the strife. 



This shell has usually been referred to Chonttes nana ; but its surface 

 presents about double the number of strios which that species possesses 

 according to the original description of M. E. de Verneuil, thirty-five 

 to forty-five being the number of stria3 upon the margin. 



The Chonetes nana has been cited by 31. de Yerneuil as occurrin<T 

 at the Falls of the Ohio, but I have not seen it among my collections from 

 that locality. 



Geological position a?id locality. In the upper beds of the limestone of 

 the age of the Upper Heldcrberg, at the Falls of the Ohio. 



Chonetes laticosta ( n. s.). 



Shell small, subhemispherical ; hinge-line a little shorter than the 

 greatest width of the shell : dorsal valve with a narrow linear 

 area and prominent dental process : ventral valve with a wider 

 area ; cardinal margin garnished by four or five tubular spines 

 on each side of the beak, which diverge very abruptly, making 

 a low angle with the hinge-line. Surface marked by about ten 

 or twelve strong rounded striae near the beak, which increase to 

 about twenty or twenty -four near the margin ; bifurcations of 

 the striee strongly marked and divergent. Shell concentrically 

 marked by fine close striee and more distant somewhat squamose 

 lamellse. The surface of the shell, when partially exfoliated, 

 presents a peculiar striato-punctate appearance. 



