37^: Costa Rica Miocene— Olsson 199 



Pecten COralliphila, n. sp, Plate 17, figures 5, 6 



Shell small, very thin and generallj^ 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 may 

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

 number, are narrow, usually somewhat 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- 

 it}^ of the shell, in harmonj^ with the external ribs. 



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



This Pecten is fairl}^ common in the coralline phases of the 

 Miocene and its associated marls and sands. It is extremely thin 

 and fragile in texture. Its sculpture resembles that of Pecten 

 gatuneyisis Toula but is much more irregular. The interspaces 

 of the left valve are of very variable width. 



Gatun Stage: Port Limo7i. 



Subgenus CHLAMYS, Bolton 



Section PLAGIOCTEN I UIVl Ball 



Pecten levicostaius Toula Plate 16, figures 5-7 



Pecten tevicostatus Toula, 1908, Jahrb. der K-K Geol. Reichsanstalt, 

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



Pecten {Ctilainys) santarosanns Bose, 1906, Boll, de Inst. Geol. de 

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

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



A scallop of the general type of Pecten ventricosus 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 



