283 



Costa Rica Miocene— Olsson m 



the base; the spirals consists of irregular sharp cords; the early 

 spire whorls carr}^ 2 main spiral cords but bordered above and be- 

 low by finer threads; the 2 principal spirals are continued on the 

 later whorls but are nearly equalled in strength by the other 

 spirals and hence lose their prominence; a short anterior canal; 

 base strongly contracted. 



Height 29, diameter 14.5, aperture 12 mm. 



Distinguished from the preceding insula by its very much 

 longer spire, more strongly contracted base and different spiral 

 sculpture. 



Gatuyi Stage: Port IJ/non. 



Genus XAMCUS Bolton 



Xancus SCOpuiUS, n. sp. I'late II, figure i 



Shell large, solid and heav}- spire nearl}' as long as the aper- 

 ture; spire-whorls 6 plus (the tip broken), strongly coronate 

 above and with large, wide, persistant ribs; the earlier spire- 

 whorls are simply shouldered or angled about the middle, but the 

 area about the upper sutures rapidly deepens and on the later 

 whorls is a deep, excavated sutural zone, above v/hich project 

 the ends of the ribs; there is a strong sutural cord and a rather 

 wide, ribbon-like band just above, forming at first a strongly ap- 

 pressed suture; the last whorl has about 7 large, wide ribs, the 

 areas between appearing as troughs or depressions; the sutural 

 excavated zone carries several irregular spiral threads which are 

 crossed by large growth-lines so that the resulting sculpture is 

 more or less cancellate, more particularly on the earlier whorls; 

 the growth-lines cross the sutural cord and upon the ribbon 

 above, become much crowded and strongly bent forwards; the 

 young shell was sculptured over the whole shell with strong 

 spirals, but with maturity, the spirals become obsolete and the 

 shell is smooth and polished; columella with 3, strong plicae as in 

 the recent scolymics; a long anterior canal, with a narrow, deep 

 umbilicus behind the spreading inner lip. 



