SOUTH AFRICAN MARINE MOLLUSKS. 171 



a retractive slant. These ribs become attenuated toward the sum- 

 mit to which they do not quite extend. They are about one-third 

 as broad as the spaces that separate them. These spaces are marked 

 near the periphery by a few, feebly expressed, fine, spiral lirations. 

 Base sculpture similar to the upper surface except that only a very 

 small portion of the smooth nuclear whorl is apparent. The ribs here 

 decrease suddenly in size as they approach the inferior suture, and 

 vanish just before reaching it. Aperture oblique, subcircular; outer 

 lip thin, showing the external sculpture within; inner lip decidedly 

 curved and somewhat reflected; parietal wall covered with a thick 

 callus. 



The type, Cat. No. 250519, U.S.N.M., comes from Port Alfred (Coll. 

 No. 1392). It shows a little more than the last whorl, and measures: 

 Altitude, 0.8 mm.; greater diameter, 1.8 mm. 



Cat. No. 250518 contains another specimen from the same locality 

 (Coll. No. 1391). 



PONDORBIS, new genus. 



Shell minute, dextral, depressed helicoid. Nuclear whorls smooth. 

 Postnuclear whorls well rounded, ornamented with distantly spaced, 

 very regular, sublamellar ribs. 



Type. — Pondorbis alfredensis. 



PONDORBIS ALFREDENSIS, new species. 

 Plate 36, figs. 1, 2, 3. 



Shell minute, depressed helicoid, yellowish white. Nuclear whorls 

 a little more than one, smooth, well rounded. Postnuclear whorls 

 well rounded, marked at regularly spaced intervals by very regular, 

 sublamellar, protractively curved, axial ribs, of which seventeen occur 

 upon the first whorl, while the one-fifth of a whorl beyond the first 

 postnuclear whorl contains ten riblets which are less strongly devel- 

 oped, and more closely spaced. Periphery strongly curved. Base 

 well rounded, openly umbihcated, showing all the whorls within, 

 marked like the spire. Aperture circular; peristome complete. 



The type, Cat. No. 250557, U.S.N.M., comes from Port Alfred 



(Coll. No. 1430). It measures: Altitude, 0.2 mm.; greater diameter, 



0.8 mm. 



Genus DISCOPbIS de Folin. 



DISCOPSIS PLANULATA Sowerby. 



Cat. No. 186883, U.S.N.M., contains two specimens from Port 

 Alfred (Coll. No. 253). Cat. No. 227784, U.S.N.M., three specimens 

 from the same locality (Coll. No. 879). Cat. No. 227785, U.S.N.M., 

 three specimens from the same source (Coll. No. 880). 



