«r4 PALEONTOLOGY OF NEW- YORK. 



9Iegaiiiboiiia spimicri (n.s.)- 



Platk XLIX. Fia. 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 diifers from the M. suborbicularis 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. 



Fig. 5 a. The left side of the cast, showing the form, the muscular scar, and elevation of 

 the beak. 



Fig. 4 6 ( by error for 5 6). Profile view from the posterior side. 



Fig. 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.] 



Megaiiibouia aviculoidca (n.s.). 



Plate XLIX. Fio. 7 a, b, and 8; and Plate XLIX A. Fio. 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 ; hinge-line straight. 



