S74 
PALAEONTOLOGY OF NEW-YORK. 
Megaiuhoiiia spinneri (n.s.). 
Plate XLIX. Pig. 5 a, b, c. 
Shell subovoid, gibbous in the middle, with a broad prominent ridge 
extending from the umbones to the base of the shell, anterior to which 
it is abruptly compressed ; posterior side less compressed ; base 
rounded : umbones prominent, much elevated above the hinge-line, 
and not incurved in the cast : muscular impressions strong and deep, 
close to the anterior margin and just below the cardinal line, pointing 
upwards (not well represented in fig. 5 a)-, the cardinal line, anterior 
to the beaks, marked by impressions of six or more transverse inter¬ 
locking teeth. 
A single specimen only, a cast, has been seen; but the characters are sufficiently 
distinctive. It differs from the M. sub orbicularis in the umbonial ridge, which extends 
on each side in a slightly curving direction, more than half way to the base : the 
beaks are more elevated and less incurved, and the muscular scars much more 
prominent. 
Pig. 5 a. The left side of the cast; showing the form, the muscular scar, and elevation of 
the beak. 
Pig. 4 b ( by error for 5 6). Profile view from the posterior side. 
Pig. 5 c. Cardinal view, showing the prominence of the muscular scars. 
Geological position and locality. In the lower beds of the Lower Helderberg 
group : Near Mohawk, Herkimer county. [ From Hon. F. S. Spinner.] 
Megambonia aviculoidea (n.s). 
Plate XLIX. Fig. 7 a, b, and 8; and Plate XLIX A. Fig. 8. 
Shell obliquely ovoid, alate on the posterior side and slightly sinuate 
below, with a small anterior lobe covering the muscular impressions, 
very gibbous in the middle and towards the umbones, compressed on 
the posterior side, and the wing not separated by a sinus from the 
body of the shell : beaks elevated and incurved; hirige-line straight. 
