No. 109.] 



159 



less salient angles : dorsal valve moderately convex ; mesial 

 fold narrow above and somewhat expanded in front, depressed 

 aad scarcely rounded, extending to the apex of the beak, and 

 marked along the middle by a faint linear depression which is 

 sometimes obsolete ; beak ard narrow area scarcely incurved : 

 ventral valve the more convex, most prominent in the umbonal 

 region, from which it slopes with a regular convex curve to the 

 front and anterior lateral margins ; beak somewhat vertically 

 compressed, arched ; sinus well defined, shallow, flat in the 

 bottom ; area moderately broad, extending quite to the ends of 

 the hinge, sharply angular along the margins between the beak 

 and the extremities, slightly arcuate backwards beyond the 

 hinge-line ; foramen of medium size, narrow triangular; lateral 

 slopes of the valves marked by about twenty-three to twenty- 

 five simple rounded plications on each side of the mesial fold 



Spieifer marcti. 



It is twenty years since the writer was commissioned by Governor Marct to the 

 charge of the Fourth Geological District of New-York, including that part of the 

 State west of Cayuga lake; and since that time, has had the satisfaction of knowing 

 him as a true and personal friend. 



