CLASS GASTROPODA 
31 
weakly impressed. Periphery of the last whorl marked by a strong keel 
to which the axial ribs extend feebly. This keel is a little nearer to the first 
post-nuclear keel than that is to its posterior neighbor. Base moderately 
long, marked by two very strong keels, which divide the space between the 
peripheral keel and the tip of the columella into three equal areas, the 
spaces between the keels being very deep and a little wider than the keels. 
Entire surface of spire and base, including the ribs and intercostal spaces, 
crossed by numerous fine, closely spaced, spiral striations. Aperture 
irregular, channeled anteriorly; posterior angle obtuse; outer lip thick 
within, thin at edge, rendered sinuous by the external sculpture; columella 
stout, strongly twisted, and reflected; parietal wall glazed with a thick 
callus. Length, 8.3; diameter, 3.1 mm. (Bartsch.) 
Type specimen in United States National Museum, No. 56906. Type 
locality, Monterey, California. 
Range. Monterey to San Diego, California. 
Described as Rissoa interfossa. 
Bittium catalinense Bartsch, 1907 
Plate 75, fig. 1 
Miscellaneous Collections, Smithsonian Institution, 50:28; PI. 57, fig. 13. 
Shell elongate-conic, milk-white. Nuclear whorls a little more than 
one, marked by two, strong, spiral cords, which divide the turns into three 
equal areas. Post-nuclear whorls shouldered at the summit, marked by 
three nodulose spiral keels ; one of these, which is a little below the summit, 
is less strongly developed than the other two on all but the last turn; on 
this turn it is practically equal to the others. In addition to the spiral keels, 
the whorls are marked by rather strong, well-rounded, axial ribs, which are 
about two-thirds as wide as the spaces which separate them. Of these ribs, 
16 occur upon the first to fifth, 18 upon the sixth and seventh, 20 upon 
the eighth, and 24 upon the penultimate turn. The intersections of the 
axial ribs and spiral cords form strong cusp-like nodules, which are sud¬ 
denly truncated posteriorly and slope gently to the succeeding cord ante¬ 
riorly. The space between the summit and the truncated end of the first 
row of tubercles forms a strong shoulder. The spaces inclosed between the 
spiral keels and the axial ribs are moderately impressed, rounded pits. 
Sutures strongly constricted, showing the greater part of the peripheral 
cord on all the turns. Periphery and base of the last whorl marked by five 
spiral cords which grow successively weaker from the periphery to the 
umbilical area. These cords are truncated on the posterior margin and 
slope gently anteriorly until they fuse with the general surface of the shell. 
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