no. 1823. MOLLVSKS OF THE GENUS CERITIIIOPSIS—BARTSCn. 341 



diameter 0.8 mm. Cat. No. 195187, U.S.N.M., contains three speci- 

 mens from the same locality. Cat. No. 122128, U.S.N.M., contains 

 two specimens dredged off Indefatigable Island, Galapagos Islands. 



CERITHIOPSIS (CERITHIOPSIS) CESTA, new species. 



Plate 39, fig. 5. 



Shell elongate-conic, chestnut brown. Nuclear whorls, three, well 

 rounded and smooth forming a slender elongate spire. Post-nuclear 

 whorls strongly rounded, marked with three feebly tuberculated 

 spiral keels between the sutures of which the posterior is at the 

 summit and the anterior at some little distance posterior to the 

 suture, the median one being a little nearer the anterior than its 

 other neighbor. The spaces between these keels are not quite as 

 wide as the keels. In addition to the spiral keels, the whorls are 

 marked with feeble, somewhat irregular axial riblets which are less 

 than half as strong as the spiral keels; of these ribs, 14 occur upon 

 the third and 32 upon the remaining whorls. These ribs render 

 their junction with the spiral cords feebly nodulose. The spaces 

 inclosed between the spiral cords and the axial ribs are feebly im- 

 pressed, squarish pits. In addition to the above sculpture, the 

 entire surface of the shell is crossed by fine incremental lines and 

 very fine spiral striations. Sutures strongly impressed, with the 

 peripheral cord showing as a slender, smooth band in all but the 

 first two whorls. Periphery of the last whorl marked by a broad, 

 depressed spiral cord which is separated from the first suprasutural 

 cord of the spire by a sulcus as wide as that separating this cord from 

 its posterior neighbor. This groove is crossed by the continuations 

 of the axial ribs. Base large, moderately rounded, marked with a 

 slender spiral cord which is a little nearer the peripheral cord than 

 the slender fasciole at the insertion of the columella. Aperture 

 irregularly ovate; outer lip thin, rendered sinuous at the edge by the 

 external sculpture showing the external sculpture within; columella 

 stout, rather long, twisted and curved ^parietal wall glazed with a 

 thin callus. The above description is based on two individuals, one 

 an adult (Cat. No. 153057, U.S.N.M.) collected at the Government 

 Jetty, San Diego, California. This has lost all but the last nuclear 

 whorl, having eight post-nuclear whorls and measuring: Length 

 5.8 mm., diameter 2.1 mm. The other is one of three specimens 

 (Cat. No. 160079 U.S.N.M.) collected at San Diego. This has the 

 nucleus and six post-nuclear whorls and measures: Length 3.2 mm., 

 diameter 1.6 mm. 



