^45 



Costa Rica Miocene — Olsson 



73 



Gaiun Stage: Bocas del Toro, Panama. 

 Drillia bocasensis, n. sp, Plate 5, figure 5 



Shell of medium size, solid; nucleus of about 2 smooth 

 whorls; post-nuclear whorls about 10; anal fasciole a narrow con- 

 stricted zone, nearl}^ filled with a large, sutural cord; axial sculp- 

 ture of large, heavy ribs, about 9 on each whorl; the ribs pass 

 from suture to suture and on the last whorl across the base to the 

 anterior canal; a large, hump-like rib is developed on the back 

 of the last whorl, formed during a resting stage; no spirals; the 

 growth-lines produce a minute but characteristic sculpture of 

 heavy, raised threads, which pass obliquely across the surface of 

 the whorls and ribs, and follow the curve of the anal 

 sinus across the fasciole; the sutural cord is finely granulat- 

 ed by the raised growth-lines; canal short but straight; outer lip 

 large, with a deep anal sinus at its posterior union with the 

 body-whorl. 



Length 22, diameter 8, last whorl 12 mm. 



This species should more properly be referred to the genus 

 Cymatosyrinx Dall, based on the Plewotoma lunata H. C. Lea, 

 a Chesapeake Miocene fossil. The form and general sculpturing 

 of bocasensis is similiar to that of many species of this group but 

 it may be recognized at once by its very peculiar, submicroscopic 

 sculpture formed by the close, heavy growth- lines. 



Gatun Stage: Bocas del Toro. 



Drillia aquaensis, n. sp. Plate 5, figure 25 



Shell small and solid; nucleus of 1+ whorls (mostly broken 

 on type specimen); post-nuclear whorls about 8; anal fasciole 

 lacking; axial sculpture of about six, large, heavy and straight 

 ribs, which pass from suture and across the base of the last whorl 

 onto the anterior canal; each set of ribs is in a straight line 

 from the canal across the spire- whorls to the apex; spiral sculp- 

 ture of about 8 impressed lines which produce a series of flat but 



