369 Costa Rica Miocene — Ousson 197 



rad from the Miocene (as Pliocene) of the State of Oaxaca, 

 Mexico. It is very distinct from the East Coast, Chesapeake 

 Miocene Oslrea sculpturata both by its form and sculpture. 



Gatun Stage: Rio Blanco. 



Coll. ^a, East Grape Pomt Creek. 



The collection also contains fragments or much decayed 

 specimens of two or more large oysters, one of which is probably 

 the gatunensis Brown and Pilsbry of the Canal Zone, and a 

 large, heavy sellcsfo7mis-\\\iQ species, possibly the Gilbertharrisi 

 Maury of the Dominican Miocene. The specimens are however 

 too fragmentary for positive determination. 



Genus PECTEN, Muller 

 Pecten gatunensis Toula Plate 16, figures 3, 4 



Peden [Flabellipectcn) gatunensis Toula, 1908, Jahrb. der K-K Geol. 



Reichsanstalt Wien, vol. 58, p. 711, pi. 29, fig. 2. 

 Pecten gatunensis Brown and Pilsbry, 191 1, Proe. Acad, Nat. Sci. 



Phila. , vol. 63, p. 365. 



Shell rather large, subcircular; the left valve is nearly flat 

 or slightly vaulted transversel}^ across the middle of the shell; 

 the right valve is moderately convex; the ears are small and 

 nearl)' equal, those of the right valve slightly flaring at the sides; 

 the right valve has 23 or 24 fairly strong ribs separated by inter- 

 spaces a little more than }i of their width; in large right valves, 

 some of the central ribs become dichotomously or trichotomously 

 divided but this feature is not always developed to the same ex- 

 tent on all shells; the left valve has 18 or 19 ribs which fade out 

 on the wide dorsal submargins; the ribs of the left valve are 

 narrow with the interspaces nearh' twice as wide; the surface is 

 covered with fine, even, raised concentric threads best preserved 

 on the left valves; interior fluted. 



Length 62, height 60 ? diameter 12.5 mm. 



62 60 ? 4 mm (left valve) 



