397 



Costa Rica Miocene -- Olsson 



125 



back of the outer lip and the corresponding shoulder to its whorls. 

 But this is not an importnnt character and recent examples may 

 sometimes lack this character. 



But few investigators v^ho have studied the West ladian 

 Miocene have failed to note the large percentage of species, close- 

 ly related or even identical with recent Pacific species, a condition 

 indicative of the union of the Atlantic and Pacific, permitting a 

 free intermingling of their respective faunas. Late during the 

 Miocene, this union was brought to a close or largely restricted, 

 and since then the Pacific element has gradually given way before 

 the encroachment and development of the West Indian. That 

 this extinction has been a gradual one is shown by the Pleisto- 

 cene deposits of Panama containg several common West Coast 

 species not known from the recent Caribbean. Such species are 

 the Peden veriiricosus Sowerb}^ and Northia northics both record- 

 ed by Dall from the Pleistocene of Panama or Costa P^ica. 



Gatun Stage: Middle Creek. 



Banana Rivei', Hill No. j. 

 Coll. 6, Red Cliff Creek. 



Genus COLIJMBELLA Lamarck 

 ColumbeHa submercatoria, n. sp. Plate 10, figures 33, 34 



Shell ovate, solid, a small conic spire and a large body- 

 whorl; whorls about 7; spire- whorls but slightly convex so that 

 the profile of the spire is nearly plane; last whorl large, broadly 

 convex about the upper 1-3 and sloping evenly below to the 

 short, produced anterior canal; sculpture of subobsolete spirals, 

 there being about 6 on the spire- whorls and about 22 on the last 

 whorl; aperture linear with a thickened outer lip, expanded in 

 the middle and finely and evenly crenulated throughout; anteri- 

 or canal short and armed with 8 strong denticles. 



Length 17, diameter 10.5, aperture 11, spire 5.5 mm. 



Closely related to the recent C. mercatoria Linn., common 

 along the northern Costa Rican coast, but difiers in its more 



