439 Costa Rica Miocene — Olsson 267 



CorbiUa {Aloidis) vieta Maury, 1917, Bull. Amer. Pal., vol. 5, p. 395, 

 pi. 39, fig. 13. 



The members of this group of CorbulcB are difficult to sepa- 

 rate satisfactorily as all are quite similiar in their characters. The 

 right valve is broad, high and coarsely sculptured with regular 

 concentric costae, while the left valve is much smaller, longer 

 than high, with its surface smooth or faintly lined with un- 

 equally distributed radial threads. 



The C . vieta was described by Guppy from the Manzanilla 

 beds of Trinidad and most authors have regarded the Erycina 

 tensa described at the same time as its left valve, an indentifica- 

 tion which is open to question. Guppy' s figure of tensa, shows 

 a Veneroid shell strongly sculptured with even radials and 

 fine concentric lines, and quite unlike the left valves of Corbulce 

 of the Aloidis section. 



? Corbula vieta from Costa Rica is identical with Maury's 

 specimens from the Miocene of Santo Domingo. It is a smaller 

 and more circular shell than the Co)'bula heterogenea Guppy 

 which we have from the Canal Zone. 



Length 6.25, height 6.50, semi-diameter 3 mm. (right 

 valve) 



Gatun Stage: Water Cay. 



Hill la, J, Banana River. 



Section CUNEOCORBULA, Cossman * 

 Corbula oropendula, n. sp. Plate 28, figures 12, 13, 14, 26, 27 



Shell small, solid, elongate, both valves of nearly equal con- 

 vexity but the the right valve somewhat larger and overlapping 

 on the left; beaks nearly central, the anterior end well rounded, 

 the posterior somewhat contracted, slightly rostrated and with 

 a well-marked keel; ventral margin more or less rounded, ter- 

 minating at is posterior end in a small sinus, just anterior to 



