CLASS GASTROPODA 
265 
columella. Aperture irregularly ovate; decidedly channeled anteriorly; 
posterior angle acute; outer lip rendered decidedly sinuous by the external 
sculpture; columella very broad at base, somewhat twisted and sinuous, 
the anterior edge slightly reflected; parietal wall glazed with a thin callus. 
Length, 4.5 ; diameter, 1.8 mm. (Bartsch.) 
Type in United States National Museum, No. 15559. Type locality, 
California? 
Range. California. 
SECTION CERITHIOPSIDELLA Bartsch, 1911 
Cerithiopsis cosmia Bartsch, 1907 
Plate 72, fig. 7 
Proceedings of the United States National Museum, 33:180. Also 40: PL 38, fig. 7. 
Shell elongate-conic, variegated with various shades of brown, white, 
and wax yellow. Nuclear whorls three and one-half, slender, lending the 
apex a mucronate appearance. First nuclear whorl smooth, second crossed 
by feeble axial riblets. The riblets increase considerably in size in the re¬ 
maining turns, where they are very regularly developed and evenly spaced. 
They are strongly protractive as they pass from suture to suture, the ex¬ 
tremity at the lower suture being considerably in advance of the extremity 
at the summit. In addition to the vertical riblets, microscopic crinkly lines 
appear on the intercostal spaces, which intersect the riblets in oblique even 
curves at right angles. The transition from the nuclear to the post-nuclear 
sculpture is abrupt, the three chief tuberculate spiral keels being present 
from the very beginning of the post-nuclear turn. On the first four post- 
nuclear turns the posterior spiral keel is less developed than the rest, but it 
increases with each succeeding turn and finally becomes the strongest of 
the three. The tubercles are the early whorls, are almost round, and slope 
abruptly, concavely posteriorly and gently well-rounded anteriorly. On 
the later whorls they are oblong, with their long axis vertical. Channels 
separating the spiral keels about as wide as the keels on the early whorls, 
less so in the later turns, curved by the low, broad, strong, backward 
slanting axial riblets. The spaces between these ribs and the spiral keels 
appear as rounded pits. Sutures well-impressed. Periphery of the last 
whorl marked by a strong spiral keel. Base well-rounded, marked by three 
equal and equally spaced spiral keels separated by equally wide and strong 
channels. The entire surface of the spire and base keels, tubercles, and 
channels are marked by microscopic lines of growth and spiral striations. 
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