LOWER HELDERBERG ROCKS. 
U77 
Megambonia obscura (n. s.). 
Plate XLIX A. Fig. 7. 
Shell subelliptical, elongate, depressed-convex; posterior slope com¬ 
pressed, not alate : beaks prominent, subacute. 
Surface marked by concentric lamellose strirn, which are nearly oblite¬ 
rated in the specimen. 
The anterior part of the shell, just below the beaks, is broken off, and the cha¬ 
racters are all obscure. 
Fig. 7. The right valve of the specimen. 
Geological position and locality. In the shaly limestone of the Lower Helderberg 
group : Schoharie county. 
Megamhonia lata (n. s.). 
Plate L. Fig. 4. 
Shell broadly ovate or suborbicular, gibbous in the middle and upon the 
umbo, and gradually sloping to the sides and base ; posterior slope 
expanded, not alate, compressed; anterior cardinal extremity abruptly 
rounded : hinge-line less than the width of the shell below. 
Surface concentrically striated. 
This species bears considerable resemblance to M. orbicularis ; but it is more 
oblique on its anterior slope, and the posterior basal portion is more expanded. 
Fig. 4. The left valve of this species. 
Geological position and locality. In the shaly limestone of the central part of the 
Lower Helderberg group : Schoharie county. 
Megainbonia oMonga ( n. s.). 
Plate L. Fig. 5. 
Shell somewhat elongate-ovate ; hinge-line short, and the shell gradually 
expanding towards the posterior extremity, gibbous from below the 
