CLASS GASTROPODA 
35 
slightly constricted. Periphery of the last whorl angulated, marked by a 
spiral cord. Base short, slightly concave in the middle, marked by six 
spiral cords, which grow successively weaker from the periphery to the 
umbilical region. In addition to the above sculpture, the entire surface of 
spire and base is marked by fine lines of growth and numerous exceedingly 
fine, spiral striations. Aperture quadrangular, channeled anteriorly; pos¬ 
terior angle obtuse; outer lip thin, showing the external sculpture within, 
rendered sinuous at the edge by the external sculpture; columella mod¬ 
erately strong, twisted, and reflected; parietal wall glazed with a thin 
callus. Length, 10; diameter, 3.3 mm. (Bartsch.) 
Type in United States National Museum, No. 195156. Type locality, 
San Pedro, California. 
Range. San Pedro, California, to San Bartolome Bay, Lower Cali¬ 
fornia. 
Bittium oldroydi Bartsch, 1911 
Plate 75, fig. 5 
Proceedings of the United States National Museum, 40:408; PI. 51, fig. 5. 
Shell very large, chestnut brown. (Nuclear whorls decollated in all 
our specimens.) Post-nuclear whorls moderately rounded, ornamented 
with three spiral keels, which are truncated on their posterior margin and 
slope gently anteriorly until they fuse with the general mass of the shell. 
These keels divide the space between the sutures into four almost equal 
parts, the space between the summit and the first keel being a little nar¬ 
rower than the rest. In addition to the spiral keels, the whorls are marked 
by slightly retractive axial ribs, of which 12 occur upon the second, 14 
upon the third and fourth, 16 upon the fifth to seventh, 18 upon the eighth, 
20 upon the ninth and tenth, and 22 upon the penultimate turn. These ribs 
extend from the summit to the suture. Their intersections with the spiral 
cords form strong, cusped nodules, which slope more abruptly anteriorly 
than posteriorly. The spaces inclosed between the spiral keels and the 
axial ribs are considerably wider than the ribs or cords and form squarish 
pits. Sutures strongly marked, showing a slender, smooth, peripheral cord 
(to which the axial ribs extend) on almost all the turns. Periphery and 
base of the last whorl well-rounded, marked by six well-rounded spiral 
cords, which grow successively weaker, and a little more closely spaced 
from the periphery to the umbilicus. Entire surface of spire and base 
crossed by numerous slender axial lines of growth. Aperture moderately 
large, channeled anteriorly; posterior angle obtuse; outer lip rendered 
sinuous by external sculpture; columella stout, flexuose, and reflected; 
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