345 



Costa Rica Miocene — OlSvSon 



173 



Genus LEDA Schumacher 



Leda Balboae Prowu and Pilsbry 



Plate 18, figure 15 



Leda Balboce Brown and Pilsbry, 191 1, Proc. Acad. Nat. Sci. Phila. , 

 vol. 63, p. 362, pi. 27, fig. 8. 



This species is fairly common in Costa Rica, but generall)^ 

 smaller than in the Canal Zone, where it frequently reaches a 

 length of 22 mm or more. Its valves are moderately convex and 

 regularly sculptured with even, close, concentric riblets which on 

 the center of the shell disk ma}^ be slightly appressed. The 

 escutcheon is well-defined and similiarly sculptured with the rib- 

 lets running parallel to the hinge margin. 



Gatun Stage: Gatun, C. Z. 



Shell small, solid, strongly convex; the beaks nearl}^ cen- 

 tral; the rostrum is short, pointed and sharply defined from the 

 rest of the shell disk by a high, cord-like ridge; the anterior end 

 is bluntly rounded and carries 2, low flexures from the beaks to 

 the anterior ventral extremity; lunule small and narow, lacking 

 the concentric ribs and sculptured with small, pustular-like 

 ridges passing at right angles to the hinge-line; the sculpture con- 

 sists of about 30 concentric riblets which are somewhat larger 

 and with deeper interspaces on the umbos; the interspaces show 

 on the umbos and along the anterior slope, fine, radial lines or 

 punctations; interior of the shell cavity deep, with a heavy 

 hinge; the anterior and posterior sets of teeth number about 13 

 or 14, are high and V-shaped. 



Length 5.75, height 4.00, semi-diameter 1.75 mm. 



Coll. I, East Grape Point Creek. 



Zome Gy Satiry Creek. 



Quit an a Creek. 



Hill No. j>. Banana River. 



Leda Davilae, n. sp. 



Plate 18, figure 20 



