Costa Rica Miocene — Olsson 



71 



A small, solid and porcellaneous species, belonging to Ball's 

 Cymatosyrinx. The sutural fasciole being absent, the ribs are 

 continuous to the upper suture and tlie surface is finely striated 

 with small, irregular spiral threads, 



Gatu7i Stage: Port Limo7i. 



Driilsa carruca n. sp. Plate 4, figure 11 



Shell of medium size, solid; whorls 7 plus (apex broken), 

 rather rapidly tapering; no fasciole; axial sculpture of about 8, 

 narrow ribs with deep and wider interspaces; the ribs commence 

 at the top of the canal and pass across the whorls to the sutures; 

 the ribs are nearly in line across the spire-whorls to the apex ; 

 spiral sculpture of slightly elevated cords, separated by wide, fiat 

 interspaces; there are about 7 spiral cords on the spire- whorl; 

 with 12 on the last whorl; aperture sub-elliptical, the outer-lip 

 somewhat thickened and a short canal. 



Height 18, diameter 7.25, last whorl ii mm. 



This shell resembles Drillia musa in its general sculpture of 

 fine, widely spaced, spiral cords. 



Gatun Stage: Coll. 4., East Grape Point Creek. 

 Driilsa Ismonensis, n. sp. Plate 5, figures 8, 9 



Shell of medium size and in form recalling D. venusta So- 

 werby; nucleus of nearly three, smooth convex whorls; post-nu- 

 clear whorls 8; anal fasciole scarcel}^ perceptible on the early 

 whorls, becoming on the later, simply a narrow, constricted zone, 

 bordering the suture; sculpture of rather numercus riblets, which 

 are abruptly bent to the left near the posterior suture on crossing 

 the constricted anal fasciole; three ribs number on the last whorl 

 about 15; the spiral sculpture consists of very fine threads; the 

 space between each pair of adjacent spiral threads is finely and mi- 

 croscopically decussated by the raised lines of growth, producing 

 a shagreening of the whole surface; in mature, shells, the last rib 

 becomes unusualh^ large and heav\ , producing a large and strong- 



