116 



[ Senate 



Chonetes hemispheric a ( n. s.). 



Pal. N.Y. Vol.iv. 



Shell transverse, semicircular, greatest width being along the 

 hinge-line; cars extending beyond the body of the shell, and 

 distinct from it, but not flattened : dorsal valve unknown : 

 ventral valve extremely ventricose, forming, without the ears, 

 nearly a hemisphere ; umbonal region gibbous, and projecting 

 a little beyond the hinge. Surface marked by numerous regular 

 rounded, radiating, occasionally bifurcating striae. 

 The distinguishing features of this shell are its hemispherical form, pro- 

 minent gibbous umbonal region, and regular rounded striae about equalling 

 the intermediate grooves. 



Geological position and locality. Schoharie grit. 



- 3 



'■ii'i 



liiiiai?' 



Chonetes hemispheeica. 



Chonetes arcuata (n. s.). 



Pal. N.Y. Vol.iv. 



Shell semicircular, greatest width being along the hinge-line, 

 ■which terminates in short, slightly depressed, triangular ears, 

 extending a little beyond the body of the shell : dorsal valve 

 profoundly concave, corresponding very nearly with the curva- 

 ture of the opposite valve : ventral valve ventricose, forming 

 an elevated arch from beak to front, sometimes having a faint 

 depression in the middle from near the umbo to the anterior 

 margin ; umbonal region prominent ; beak incurved, and rising 

 a little above the hinge -line. Surface marked by numerous 

 fine regular striee, which increase both by bifurcation and im- 

 plantation, and are crossed by very fine obscure concentric lines. 



