NO. 2250. NEW MARINE SHELLS FROM PANAMA— BARTSCH. 575 



two, well rounded above, the first one and a half marked with a strong 

 keel about one-third of the distance between the suture and the 

 periphery, anterior to the suture. This keel becomes enfeebled on 

 the last half of the last whorl and practically completely disappears 

 before the edge of the aperture is attained. In addition to this keel 

 the upper surface is marked by rather distantly spaced, slender, re- 

 curvedly slanting axial riblets, of which 19 occur upon the first 

 turn and 22 upon the last; these riblets are about one-sixth as wide 

 as the spaces that separate them in the region of the keel and much 

 more distantly spaced at the periphery. In addition to the axial 

 sculpture, the whorls are marked on the upper side by slender, raised 

 spiral threads, which are separated by fine, incised lines; of these 

 threads 50 occur between the summit and the periphery of the last 

 whorl. Sutures strongly impressed. Periphery of the last whorl 

 strongly carinated. Base very broadly, openly unbilicated, marked by 

 the continuations of the axial riblets which become condensed within 

 the umbilicus and somewhat irregularly spaced. The spiral sculp- 

 ture on the base is even finer than on the upper surface. In fact, it 

 is so fine that we have found it best not to indicate it in our sketch. 

 Aperture very large, oblique; with a decided angle at the periph- 

 ery and another at the junction of the columella and the basal lip; 

 parietal wall very narrow, covered by a thin callus. 



The type (Cat. No. 216920, U.S.N.M.) comes from shell siftings 

 of sand and worm burrows collected at Punta Paitilla, near Panama 

 City. It measures — altitude, 1 mm. ; diameter, 2.2 mm. 



EXPLANATION OF PLATE 88. 



Figs. 1, 2, and 3. Discopsis argentea. 



4. Cylichnella zeteki. 



5. Odostomia (ChrysalUda) zeteki. 



6. 7, and 8. Heliacus panamensis. 



9, 10, and 11. Discopsis panamensis. 



