283 Costa Rica Miocene— Oi.sson 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 strongl}^ 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. 



Gahai Stage: Port Union. 



Genus XANCUS Bolton 

 XasiCUS SCOpuiuS, n. sp. Plate II, figure i 



Shell large, solid and heavy; spire nearly 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 simpl}^ shouldered or angled about the middle, but the 

 area about the upper sutures rapidlj^ deepens and on the later 

 whorls is a deep, excavated sutural zone, above which 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 scolymns; a long anterior canal, with a narrow, deep 

 umbilicus behind the spreading inner lip. 



