2IO Bulletin 39 382 



ince of Coltoii, Panama, near the Canal Zone. It frequentlj'' 

 gives rise to important zones in the lower part of the Gatun for- 

 mation, where it occurs in large numbers associated with Peden 

 levicostatiis Toula. 



The specimens are generally large, thin-shelled, smooth and 

 irregular in form, due to the object on which they were attach- 

 ed. The}' average for the upper valves about 35 mm in 

 height. 



Anomia simplex appears as a Miocene fossil in the eastern 

 United States for the first time in the St. Mar^^'s formation of 

 Maryland in the upper part of the Lower Chesapeake. It occurs 

 throughout the Upper Chesapeake Miocene and Pliocene and 

 passes into the recent fauna. Locally as a fossil it ma^^ become 

 very abundant, as at the base of the Pliocene overlying Upper 

 Chesapeake Miocene along the shores of Lake Waccamaw, 

 North Carolina. It occurs rarely as a Miocene fossil in Santo 

 Domingo, where it has been recorded by Gabb and Maury. In 

 Mexico, it occurs in the Miocene of Santa Rosa, Vera Cruz as 

 figured by Bose. 



Gatiai Stage: Several localities, Prov. of Colon, Panama. 



Middle Creek. Comadre Creek. 



Hone and Hotel Creeks. 



Hill No. 2, Banana River, Soury Creek, etc. 



Genus PLACUNANOMIA, Broderip 

 Placunanomia lithobleta Dall Plate 21, figures 3, 4, 5 



Placunanoinia litJiobleta Dall, 1898, Trans. Wagner Free Inst. Sci. ,vol. 



3, pt. 4, p. 778. 

 Placunanomia lithobleta Maury, 1917, Bull. Amer. Pal., vol. 5, p. 356, 



pi. 34, figs. I, 2. 



The Costa Rican specimens are frequently widely plicate, 

 nearly as much as in the Duplin Miocene P. plicata Tuomey and 

 Holmes, but the surface is marked with fine, wavy, radial threads 

 so that even very small fragments of this species are very easily 

 recognized. It occurs in the Miocene of Jamaica, its type local- 

 ity, and in the Miocene of Santo Domingo. 

 Gatun Stage: Hill 3, Banana River. 



