341 Costa Rica Miocene— Olsson 



on the base of the last whorl; the spirals do not cross the ribs so 

 that the summit of the ribs are left nearly smooth; aperture 

 small with a short, slightly twisted anterior canal. 



Length ii, diameter 4 mm. 



A small species sculptured like the D. elegans Conrad of 

 the Chesapeake Miocene of Virginia, but with more numerous 

 and more closely spaced ribs. 



Gatun Stage: Port Linion. 



Drillia musacina, n. sp. Plate 5, figures 27, 28 



Shell small, slender; the nucleus of about 2 whorls, the ist 

 blunt, convex and smooth, followed by the 2nd which is strongly 

 carinate; there are 7 post- nuclear whorls of slightly convex pro- 

 file; the fasciole is a narrow band on which the ends of the ribs 

 become strongly deflected to the left; the axial sculpture of about 

 16, narrow ribs on the last whorl; the ribs are continuous across 

 the spire-whorls to the upper sutures but become bent and 

 strongly deflected on the fasciole; on the last whorl, the ribs are 

 continued to the base of the canal; the spirals vary somewhat 

 in strength but are usually subregular spiral bands of which there 

 are 7 or 8 on the spire whorls and about 14 on the last whorl and 

 the canal; the back of the last whorl is strongly humped; the 

 outer lip was probably thin (broken in all our specimens) ; canal 

 short, straight. 



Length 9, diameter 2.75, last whorl 5.00 mm. 

 A small species abundant in the Gatun beds of the Banana 

 River. 



Gatun Stage: Hill la, Banana River. 

 Hill J , Banana River. 



Drillia estrellana, n. sp. Plate 10, figures 31, 32 



Shell very small, solid, porcellaneous; slender with a long 

 spire and a short body-whorl; nucleus small of 2 smooth, convex 



