OF CONCHOLOGY. 199 



DESCRIPTIONS OF NEW TERTIARY FOSSILS, "WITH NOTES 

 • ON TWO GENERA OF LAMELLIBRANCHIATA. 



BY T. A. CONRAD. 



MA CO MA, Leach. 

 M. SUBLINTEA, Conrad. PI. 11, fig. 5. 



Suboviil or subtriangular, inequilateral, compressed ; anterior 

 side shorter than the posterior, subcuneiform ; posterior dorsal 

 margin slightly curved, oblique, regularly rounded at the ex- 

 tremity ; ventral margin slightly curved ; disk with minute con- 

 centric slightly impressed lines. 



Locality. Vicksburg. Oligocene. 



ABRA, Leach. 

 A. PROTEXTA, Conrad. Plate 11, fig. 4. 



Elliptical, elongated, inequilateral, compressed, sinuous ; disk 

 •widely contracted. 



Locality. Vicksburg. Oligocene. 



Of this species one valve, the left, is all that I have seen. It 

 is remarkable for its length. 



AXIN^A. 

 A. BELLA, Conrad. Plate 13, fig. 1. 



Subovate, convex, equilateral ; ornamented with fine, close, 

 regular concentric lines ; ribs prominent, acute and entire on 

 the umbo and thence dividing into two, and sometimes three, 

 narrow ribs ; interstices with each a rib, and sometimes one or 

 two lines, all which disappear on the umbo ; marginal teeth nar- 

 row, numerous, closely-arranged ; hinge series in two subequal 

 continuous curves. 



Locality. Day's Point, Virg. Miocene. 



Among recent species the nearest approach to the hella is A. 

 parcipicta, Reeve. Monog. fig. 14. 



