466 



NORTH AMERICAN INDEX FOSSILS. 



Upper Eocenic (Jacksonian): Mississippi, Alabama, Louisiana. 

 Lower Oligocenic (Vicksburgian): Florida and Mississippi. Mio- 



FlG. 620. a, Ostrea selheforvris, lower valve, X/^! &> O. compressirostra, lateral 

 view. (Md. Surv. ) 



cenic : Maryland (Choptank) and North Carolina. Pliocenic : 

 Florida. 



284. 0. percrassa Conrad. (Fig. 621, c.) Miocenic. 



Porous and vesicular, of light weight though very thick. Much 



Fig. 621. a, 6, Ostrea trigonalis i lower valve, X l A » r > ®- percrassa, upper 

 valve, XX- ( Md - Surv 



like 0. trigonalis from which it differs in its somewhat larger size 

 and broader outline. 



New Jersey, Maryland (Calvert), Florida. 



