365 Costa Rica Miocene — Olsson 193 



bonal angle are smooth, beyond which on the posterior-dorsal 

 slope the ribs again become beaded as they approach the dorsal 

 margin; the interspaces on the right valve are wide, and on the 

 shell disk anterior to the umbonal angle they carry a fine, but 

 often faint interstitial thread; the intervals are otherwise smooth 

 or finely etched with concentric lines; hinge-lines straight with 

 numerous small, vertical teeth and a wide, smooth cardinal 

 area. 



IvCngth 18, height 18, semi-diameter 9.5 mm. 



A smaller species than the following {Hiyidsi) and easily 

 distinguished by the interstitial thread of its right valve. It is 

 much less common than the other two species. 



Named for Dr. E. R. I^loyd, formerly of the United States 

 Geological Survey, and who was a member of the first Explora- 

 tion Party of the Sinclair Oil Company in Panama and Costa 

 Rica. 



Gatun Stage: Hill j, Banana River. 

 Zone 5, Red Cliff Creek. 

 Coll. 7, Pumbri Creek. 



Area Hindsi, n. sp. Plate 24, figures 7-9 



Shell small or of medium size, cordiform and similiar in out- 

 line to the preceding species but larger; umbos high and wide, 

 and but slightly anterior to the middle; the left valve has about 

 26 strongly nodulated ribs, separated by interspaces of slightly 

 greater width; the first 9 or 10 ribs of the right valve are nodu- 

 lated, followed by smooth ones to the umbonal angle, beyond 

 which the remaining 7 become nodulated as they approach the 

 dorsal margin; interspaces wider than the ribs, smooth and 

 without an}^ interstitial thread; hinge-line straight with numer- 

 ous, small vertical teeth and a wide, smooth cardinal area; on 

 some shells the ligamental area may carry one or two, small 

 diamond-shaped grooves. 



Length 24, height 25, semi-diameter 14 mm. 



A much larger species than the Lloydi and without anj^ in- 



