38i Costa Rica Miocene— Olsson 109 



crossed by heavj-, ridge-like, spiral cords, which on crossing the 

 deep interspaces between the ribs, form small, sunken pits, so 

 that the sculpture appears coarsely trellised. 



Gatun Stage: Toro Cays. 



Genus PTYCHOSALPI^IX Gill 

 Ptychosaipiiix? dentalis, n. sp. Plate 15, figures 14, 18 



Shell buccinoid with convex, cancellated whorls; whorls 

 about 6, with channelled sutures so that the whorls appear nar- 

 rowly shouldered above; the sculpture is predominantly spiralled, 

 the penultimate whorl with 7 strong spiral cords with interspaces 

 2 or 3 times their width; small spiral threads may appear in the 

 interspaces; the last whorl has 14 or more spirals and the wide 

 interspaces with one or more finer threads; the spirals are cross- 

 ed by coarse wavy lines of growth, producing a sub-cancellate 

 sculpture; the aperture is subovate; a well-developed siphonal 

 sinus; the columella carries a single sharp plication at its lower 

 end; the outer lip is slightly thickened and bears within about 

 12, small, narrow lirse. 



Height 28, diameter 11, aperture 16 mm. 

 The generic relation of this interesting species is very much 

 in doubt. It has the general form of Coniijiella, but its colum- 

 ella is provided with a strong anterior plication. In this regard 

 it agrees with Ptychosalpinx of which there are several species in 

 the Chesapeake Miocene. The apex of dentalis, appears to have 

 been pointed and sharp, although all of our specimens have the 

 tip of the spire very much weathered. True Ptychosalpinx is 

 characterized by a large, convex and blunt nucleus and the outer 

 lip is thin and smooth within. The outer lip of dentalis is slight- 

 ly thickened and internally finely lirated. 



The P f dentalis, is a very characteristic fossil of the Denta- 

 liimi zone of the Upper Uscari formation. 



