52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I25 



PYRGISCUS HEBEAE, new species 

 Plate 9, figures 4a, b 



Shell small, turrited, cream-yellow. The nucleus consists of about 

 2.5 strongly rounded whorls that form a rather elevated helicoid 

 spire whose axis is at right angles to that of the postnuclear whorls, 

 in the first of which it is only slightly immersed. The postnuclear 

 whorls are flattened and marked by moderately strong vertical axial 

 ribs, of which 12 are present upon the first and second, 13 upon the 

 third, 14 upon the fourth, 16 upon the fifth, 18 upon the sixth, 20 

 upon the seventh, and 22 upon the last whorl. These ribs are of the 

 same strength from the summit to the periphery. The intercostal 

 spaces are about as wide as the ribs and are marked by eight spiral 

 pits that differ much in width and spacing and are best described by 

 our figure 4b, on plate 9. The suture is not strongly impressed and 

 is rendered wavy by the summits of the axial ribs. The base is hemi- 

 spherical and smooth. The aperture is obliquely elongate-oval ; the 

 columella is straight and provided with an oblique fold a little anterior 

 to its insertion ; the outer lip is thin and evenly curved. 



The type, U.S.N.M. No. 561660, comes from the Pliocene deposits 

 of North St. Petersburg, Fla. It has 8.5 postnuclear whorls and 

 measures: Length 3.2 mm., diameter 0.9 mm. 



The less regularly elongate-conic shape, as well as the different 

 spiral sculpture of the intercostal spaces, easily distinguishes this 

 species from Pyrgiscus aesoni (below). 



PYRGISCUS AESONI, new species 



Plate 9, figures 7a, b, c 



Shell small, turrited, very regularly elongate-conic, cream-colored. 

 The nucleus is small, and consists of about 2.5 strongly rounded 

 whorls that form a moderately elevated helicoid spire, whose axis 

 is at right angles to that of the postnuclear spire. The postnuclear 

 whorls are flattened and marked by very regular, strong, retractively 

 slanting axial ribs, which are obscure upon the first whorl, while the 

 rest of the whorls in the young cotype show 16. The adult fragment 

 of the other cotype also shows 16 ribs upon all its whorls. These ribs 

 are equally strong from the summit to the periphery. The intercostal 

 spares are a little narrower than the ribs and are crossed by eight 

 spiral pits that differ greatly in width and spacing and are best de- 

 scribed by our sketch on plate 9, figure 7c. The suture is not strongly 

 impressed and is rendered wavy by the summits of the axial ribs. 



