THE NAUTILUS. 



VOL. XVIII. OCTOBER, 19O4. No. 6. 



A NEW OYSTER FROM THE EOCENE OF ALABAMA. 



BY T. H. ALDUICH. 



OSTKEA ARROSIS 11. sp. PI. Ill, figs. 1-4. 



Shell oval, lower valve thick and heavy, upper valve thin. Sur- 

 face oflower valve strongly ribbed, ribs very numerous, close-set and 

 cross marked by growth lines, inner edge of lower valve is scalloped. 

 Both valves have a large, muscular scar, not central. The beak is 

 strong, making a stout hinge in the lower valve, much smaller in the 

 upper. The upper valve is smaller, fitting into the other ventrally 

 above the crenulations ; its surface is generally covered with tine, 

 raised lines of growth ; interior with crenulations near the beak, be- 

 coming obsolete on the ventral margin. Size of old specimens 125 

 to 140 mm. from be*ak to ventral margin, about one-fifth less at right 

 angles across the shell. 



Locality Fleming's Mill, on Pea River, in Southeast Alabama, 

 from the Nanafalia horizon. 



Remarks Figures 1 and 2 are the exterior-and interior of a large, 

 lower valve ; fig. 4, upper valve of young shell ; fig. 3, young shell 

 with both valves in place. In old shells the ribbing becomes obso- 

 lete on the beak, and in some examples the beak is bent, strongly to 

 one side. This oyster seems to be the precursor of 0. sellae.fonms 

 Con. Some young examples occur in the Alabama River lignitic, 

 but the full-grown shell has not before been found that I am 

 aware of. 



