Bulletin 39 394 



Gatun Stage: Headwater of Middle creek. 



Old Man Sam creek, i mile sotith of the beach. 



Subgenus HERE, Gabb 



Section CAVILUCINA, Fischer 



Phacoides trisulcatus Conrad 



Lncina tristclcata Conrad, 1841, Trans. Amer. Assoc. Nat. andGeoL, 



vol. I. p. no. 

 Lucina trisulcata Conrad, 1845, Fossils of the Medial Tertairy, p. 71, 



pi. 40, fig. 5. 

 Phacoides {Cavilucina) trisulcattis Dall, 1903, Trans. Wagner Free 



Inst. Sci., vol. 3, pt. 6, p. 1369. 



Few specimens from the Gatun of Middle Creek. They 

 are identical with typical specimens from the Chesapeake Mio- 

 cene of the eastern United States. The species also occurs in the 

 recent fauna. 



Gatmi Stage: Middle creek. 



Old Man Sam creek. 



Subgenus LUCmiSCA, Dall 

 Phacoides costaricensis, n. sp. Plate 32, figure 5 



Shell subcircular, moderately thick and but slightlj' convex: 

 beaks small and inconspicuous, a little in front of the middle; 

 dorsal area impressed and well defined; sculpture consists of 

 strong, regular, radial threads, widely separated hy interspaces 

 2 or 3 times the width of the threads themselves; they are cross- 

 ed by distant but regular concentric ridges, the intersection form- 

 ing small beads or granulations, strongest on the anterior and 

 posterior extremities; the lunule is narrow, lanceolate and with 

 the concentric sculpture predominanting; interior of shell cavity 

 rather shallow, the ventral margin coarsely serrated by the ex- 

 ternal sculpture. 



