441 



Costa Rica Miocene — Olsson 



269 



coarsely concentrically grooved, the two valves being sculptured 

 alike. 



Gatun Stage: Port Livio7i. 



Corbula hexacyma Brown and Pilsbry Plate 21, figures 12, 13 



Corbula hexacyma Brown and Pilsbry, 191 2, Proc. Acad. Nat. Sci. 

 Phila., vol. 64, p. 518, pi. 26, fig. 4. 



A species of the Gatun beds of the Central Zone. The shell 

 is rather large, solid and with its valves similiary sculptured 

 with a few, deep, wave-like, concentric ribs. Its right valve is 

 slightly more convex than its left. Our specimens measure: 



Length 20, height 14, diameter of the left valve 6.00 

 mm. 



Length 20, height 13.50, diameter of the rigth valve 

 5.75 mm. 

 Gatun Stage: Gattin^ C. Z. 



Corbula orosi, n. sp. Plate 21, figures 9, 10 



Shell elongate, convex with the low inconspicuous beaks 

 about the middle of the shell, so that the posterior and anterior 

 ends of the shell are about equal in length; the right valve is 

 slightly larger and its basal margin folds over slightly that of 

 the left valve; anterior end rounded, the posterior narrow and 

 more pointed but with the keel only very poorly developed; the 

 surface is finely and evenly concentrically ribbed and both valves 

 are similiarly sculptured; no lunule. 



Length 20, height 11. 5, diameter of both valves 9.5 mm. 



A rather large species with nearly equally convex valves; 

 surface sculptured with fine, regular, concentric ribs. It 

 resembles the C. sarda Dall, from the Chipola Miocene but is 

 much larger. 



Gatun Stage; Hill No. j, Baiiana River. 



