417 Costa Rica Miocene — Olsson 245 



Gatun Stage: Gatun, C. Z. 

 Banana River. 

 Coll. 6, Estrella River. 



Clhione costaricensis, n. sp. Plate 32, figure 4 



Shell of moderate size, convex, ovate-trigonal; the dorsal 

 portion of the type specimen is lacking; the surface is sculptured 

 with fine, subregular, concentric lamellae spaced on the center of 

 the shell disk about .75 mm apart; the interspaces and the ven- 

 tral surfaces of the larnellae are marked with regular, incised lines 

 forming radial bands of an average width of .40 mm; a faint rad- 

 ial sinus extends from the beaks to the posterior; ventral margin 

 of the shell is slightly arcuate at its posterior end; interior of 

 ventral margin finely crenulated. 



Length 34, height 29, diameter of the right valve 10 

 mm. 



This shell will be distinguished from the other Costa Rican 

 Chiones by its more crowded, concentric, lamellae and regular, 

 radial striae. The striae occur on the ventral faces of the lamel- 

 lae and on their interspaces. 



Gatun Stage: Hill No. j, Banayia River. 



Section LIROPHORA, Conrad 



Chione mactropsis Conrad Plate 30, figures 7, 8 



Gratelupia? mactropsis Conrad, 1856, Pacific R. R. Reports, vol. 5, p. 



328, pi. 6, fig. 54. 

 Chione {Lirophofa) mactropsis Dall, 1903, Trans. Wagner Free Inst. 



Sci., vol. 3, pt. 6, p. 1294. 

 Chione {Lirophora) mactropsis Brown and Pilsbry, 1911, Proc. Acad. 



Nat. Sci. Phila., vol. 63, p, 369. 

 Chione {Lirophora) ulocyma Brown and Pilsbry, 1911, Idem. p. 369. 



Not of Dell. 1903. 



Until the construction work on the Panama Canal had com- 

 menced in earnest, the abundant and finely preserved fossils of 



