OBISKANY SAIfDSTONE. 4ftl' 



Megaiubonia bellistriata ( n. s.)> 



Plate CIX. Fig. 4. 

 Shell obliquely ovate, symmetrically convex, regularly rounded below, 



and gradually narrowing above. Anterior wing large, convex. 

 ScKFACE marked by fine subequal rounded or somewhat flattened strias, 



which are wider than the spaces between them, increasing by inter? 



stitial additions, and finely crenulated by concentric striae. The radiating 



ribs on the wing are coarser than on the body of the shell, and the 



concentric striae become lamellose. 



The specimen is a mould, in sandstone, of the left valve, and the figure is drawn 

 from a cast made in this mould. The wing is convex, like those of the genus gene- 

 rally, and the hinge-line and posterior slope are unknown. 



Fig. 4. A cast of the left valve, from a monld of the exterior in sandstone. 

 Another specimen, which is a distorted cast of the interior of an individual, apparently of 

 this species, shows faint radiating striae and a long posterior slope, without defined wing. 



Geological position and locality. In the Oriskany sandstone : Albany and Scho» 

 harie counties. 



Meganibonia lamellosa ( n. s.). 



Platk CIX. Fio.5 & 6. 



Shell obliquely ovoid, very gibbous in the middle and towards the umbo ; 

 the body of the shell rather abruptly narrowed above the middle. 

 Anterior wing short, rounded, very convex, separated from the body 

 of the shell by a broad rounded depression, leaving a sinus in the 

 margin. Posterior wing broad triangular, extending more than two- 

 thirds the entire length of the posterior slope ; its junction with the 

 body of the shell marked by a depression. 



Surface marked by concentric lamellose striae, which, on some parts of 

 the specimens, are very prominent. Faint remains of radiating striae 

 are sometimes perceptible on the casts. 



Fig. 5. The left valve of a specimen of this species. 



Fig. 6. The left valve, showing a proportionally more extended wing than the preceding. 



Geological position and locality. In the Oriskany sandstone : Albany and Scho" 

 harie counties; and at Oriskany lalls, Oneida county, New- York. 



