27© 
PALAEONTOLOGY OF NEW-YORK. 
Megambonia mytiloidea (n. s.). 
Plate XLIX A. Fig. 3 a, b. 
Shell subovoid, slightly inequivalve (from accident or otherwise), gib¬ 
bous in the middle : nmbones prominent, acute, scarcely incurved; 
margins regularly curvilinear, without visible alation on the posterior 
side or projection in front. 
Surface marked by fine lamellose concentric strim. 
The shell is exfoliated partially from the right valve, and entirely from the 
opposite valve. 
Fig. 3 a. The right valve of the specimen. Fig. 3 b. Profile view of the same. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Helderberg mountains. 
Plate XLIX A. Fig. 4 a, b. 
Shell obliquely subovoid, the right valve a little the more prominent, 
very gibbous in the middle and upper portions : uinbones prominent, 
rounded, incurved over the hinge-line, and bending forward ; posterior 
cardinal margin compressed, not alate, abruptly rounded in front, with 
a more prominent lobe covering the muscular scar : a scarcely per¬ 
ceptible sinus separates this lobe from the body of the shell. 
Surface marked by lamellose concentric striae, with some stronger lines 
of growth, and by fine equal radiating striae [only visible on the right 
valve of the specimen.] 
The slight inequality of the valves does not appear to be due to accident; and 
the same character holds true of the two preceding species, the right valve being a 
little less convex. 
Fig. 4 a. The left valve of the specimen. 
Fig. 4 b. Profile of the same, looking upon the cardinal line. The beak of the right valve 
is broken off. 
Geological position and locality. In the lower part of the Lower Helderberg group : 
Schoharie county. 
