412 PROCEEDINGS OF THE NATIONAL MUSEUM. vol.40. 



and fourth, 16 upon the fifth to seventh, and 20 upon the penultimate 

 turn. The intersections of the axial ribs and the spiral cords form 

 narrow, elongate tubercles the long axes of which coincide with the 

 spiral sculpture. The spaces between the spirals appear as broad, 

 strongly incised lines. Sutures moderately impressed. Periphery of 

 the last whorl marked by a spiral cord equal to the stronger cords 

 between the sutures. Base well rounded, ornamented with 10 sub- 

 equal and subequally spaced spiral cords. Aperture moderately 

 large, channeled anteriorly; posterior angle obtuse; columella stout, 

 twisted, oblique, and reflected. 



The type (Cat. No. 165265, U.S.N.M.) has the last eight post- 

 nuclear whorls, which measure: Length 16.8 mm., diameter 7 mm. 

 It comes from the Fernando Formation, Lower Pliocene, at the Wal- 

 dorf asphalt mine, 3 miles southeast of Guadaloupe, Santa Barbara 

 County, California. 



Named for Dr. Ralph Arnold of Pasadena. 



BITTIUM MEXICANUM, new species. 



Plate 58, fig. 1. 



Shell elongate-conic, brown. Nuclear whorls decollated. Post- 

 nuclear whorls well rounded, appressed at the summit, marked on the 

 first four turns by four spiral cords which divide the space between 

 the sutures into four equal parts; the first of these cords is at the 

 summit. The first basal cord becomes apparent in the suture of all 

 the turns and gives the shell the appearance of having five cords 

 between the sutures on the spire. Beginning with the fifth whorl, a 

 slender, spiral cord appears immediately below the cord at the sum- 

 mit and increases rapidly in strength until, on the last whorl, it is 

 about half as strong as the cord at the summit. Another intercalated 

 cord begins on the sixth whorl, between the fourth cord and the 

 basal cord. In addition to the spiral sculpture, the whorls are 

 marked by slender, rounded, axial ribs, of which 20 occur upon the 

 third, 16 upon the fourth to sixth, and 30 upon the penultimate 

 turn. Intersections of the axial ribs and spiral cords form low, 

 rounded tubercles, while the spaces inclosed between them are rec- 

 tangular pits, having their long axes parallel with the spiral sculp- 

 ture on all but the last whorl; on this they are squarish pits. Sutures 

 strongly constricted. Periphery of the last whorl marked by a 

 channel. Base moderately long, concave, marked by six feeble, 

 spiral cords, grouped in two series of three, one of which is imme- 

 diately below the periphery and the other surrounds the base of the 

 columella. Aperture irregularly ovate, channeled anteriorly; pos- 

 terior angle acute; outer lip thin, showing the external sculpture 

 within, rendered sinuous try the external sculpture; columella oblique, 

 somewhat twisted, and reflected. 



