339 Costa Rica Miocknb — Olsson 167 



smaller intermediate ones in the interspaces; the ribs become 

 gradually obsolete with age and the later portions of full-grown 

 shells are nearly smooth; fine transverse lines of growth cross the 

 surface and are best seen on the earlier portions of the shell; 

 operture oblique. 



Length 60, diameter 12 mm. 



This large Dentaliuvi is abundant and very characteristic of 

 certain conglomeritic zones in the Upper Uscari shales. There it 

 occurs associated with a small but very distinctive fauna, includ- 

 ing the Ptychosalpinx ? dentalis, Sconsia cocleana and Staphella 

 costaricayia and other species. When complete, the Deiitaliuni 

 uscat-ianum frequently reached a length of no mm or more. 



All our specimens are unfortunately lacking in the apical 

 tip. In general sculpture, it recalls the Dentalium Jioridense 

 Henderson dredged from 35 to no fathoms of water oil Florida 

 and in the West Indies, but the taper of the shell is more gradual 

 and the sculpture more irregular, becoming obsolete with age. 

 Bose'"^ has described a large species as Dentalium rwtosum from 

 the Miocene of the Tehuantepec Peninsula. In that species, the 

 ribs number about3i, are very regular with deep interspaces, and 

 ribs are finel}' etched by transverse lines of growth. 



Uscari Stage: Coco Plum, Panama. 

 Rio Codes. 



Margarita — Old Harber trail. 

 Covtadre Creek. 

 Puvibri Creek, etc. 



*Boll. Inst. Geol. do Mexico, No. 22, p. 55, pi. 3, figure i, 1906. 



