Costa Rica Miocene— Olsson 



199 



Pecten coralliphiSa, n. sp, 



Plate 17, figures 5, 6 



Shell small, very thin and generally translucent; broader 

 than high; right valve moderately convex, the left concave with 

 raised submargins; ears small and subequal; sculpture of the 

 right valve of about 23 low, flat ribs, with flat interspaces a 

 little more than the width of the ribs; some of the ribs ma\^ 

 become divided medially; the ribs of the left valve, about 20 in 

 number, are narrow, usuall}^ som.ewhat irregularly spaced so 

 that their interspaces are of variable width and new ribs may 

 occasionally appear in the wider interspaces near the ventral 

 margin; surface in addition finely sculptured with even, raised 

 concentric threads; interior of the shell fluted well into the cav- 

 ity of the shell, in harmony with the external ribs. 



Length 34, height 29, semi-diameter 4 mm (right valve) 



This Peden is fairly common in the coralline phases of the 

 Miocene and its associated marls and sands. It is extremel}^ thin 

 and fragile in texture. Its sculpture resembles that of Pecten 

 gatunensis Toula but is much more irregular. The interspaces 

 of the left valve are of very variable width. 



Gatun Stage: Port Lhnon. 



Peden tevicostatus Toula, 1908, Jahrb. der K-K Geol. Reichsan stall, 

 Wien, vol. 58, p. 713, pi. 26, figs. 4, 5, 6. 



Peden {Chlainys) santarosafius Bose, 1906, Boll, de Inst. Geol. de 

 Mexico, numero 22, p. 73, pi. 6, figs. 3,4, '^Pecten {Chlainys) 

 santarosanus Bose, op. cit.. p. 23, pi. i, figs, i and 4, 2 and 5. 



A. scallop of the general tj^pe of Pecten ve?itricos2cs Sowerby; 

 both valves equally and strongly convex; ribs about 21, which 

 are square or rectangular in section on the umbos and with deep 

 interspaces; the ribs generally flatten or become more rounded in 



Subgenus CHLAIVIYS, Bolton 



Section PLAOiOCTEhllUiVi Ball 



Pecten levicostatus Toula 



Plate 16, figures 5-7 



