357 Costa Rica Miocene — Olsson 185 



of Oronli Creek in the Talaraanca Valley (probably the Uscari 

 shell). It is like A. dariensis, in form, but with more central 

 beaks and umbones and simple ribs. We have not seen this 

 species. 



Gatun Stage: Gahtn and Mt. Hope, C. Z. 

 Wvter Cay. 



Area actinophora Dall Plate 23, figs. 7, 8; Plate 25, fig. 3 



Scaphafca {Scapharca) acitnophora Dall, 1898, Trans. Wagner Free 



Inst. Sci., vol. 3, pt. 4 p. 647, pi. 33, fig. 26. 

 Scapharca {Scapharca) actinophora Sheldon, 1916, Paleont. Amer. , 



vol. I, p. 50, pi. II, fig. 13. 



A larger species than the dariensis, with broad, wide umbos. 

 The ribs number 36 to 40, are narrow and separated by inter- 

 spaces of a little more than their own width. These interspaces 

 are generally finely ornamented by regular, even, concentric 

 threads. The ribs are simple and on the left valve, usually strong- 

 ly beaded or granulated throughout, becoming wider and smooth- 

 er on the posterior portion, or with the granulations only on 

 their edges, so that the ribs appear as if mesially depressed. The 

 ribs of the right valve are less strongly beaded and may become 

 quite smooth, especially on the center of the shell disk. 



Its ventral margin is gently curved to the rounded and not 

 pointed posterior extremity. 



It is a common species at Mt. Hope in the Canal Zone, but 

 it also occurs but less abundant in Western Panama and in 

 Costa Rica. 



Gattm Stage: Mt. Hope, C. Z. 



Water Cay, Panama. 

 Zone 4, Red Cliff Creek, C. R. 

 Coll. J, Hone Walk Creek, C. R. 

 Hill I Banana River, C. R. 



