162 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
only half of the last whorl projects. Post-nuclear whorls separated by 
broad, deep sutures; well-rounded between the sutures, where they are 
ornamented by four, strongly tuberculate, spiral ridges; the spiral connec¬ 
tions between the tubercles are equal to the axial connections or ribs, of 
which sixteen appear upon the second, eighteen upon the thirtieth, and 
twenty upon the penultimate whorl. The spaces inclosed between the axial 
ribs and the spiral connections which join the rounded tubercles are deep, 
squarish pits. The axial ribs extend strongly across the deep peripheral 
channel and stop at the first subperipheral keel. Base moderately long, 
well-rounded, marked by five equal and subequally spaced, well-raised, 
strong, spiral keels, and a sixth, much broader, low, and rounded at the 
columella margin. The grooves between the keels are equal to the width 
of the keels near the periphery, but diminish in breadth successively from 
the periphery to the umbilical area. They are crossed by numerous, 
slender, raised, axial threads, which extend up on the sides of the spiral 
keels, but do not cross them. There are about five of these threads between 
each two ribs in the first subperipheral channel; aperture oval, somewhat 
effuse anteriorly; posterior angle acute; columella re-enforced by the 
attenuated base, against which it appears like a thickened callus, provided 
with a moderately strong oblique fold at its insertion; parietal wall 
covered by a thick callus, which joins the columella with the posterior 
angle of the aperture. Length, 3; diameter, 1.3 mm. (Dali and Bartsch.) 
Type in United States National Museum, No. 196281. Type locality, 
off Del Monte, Monterey Bay, California. 
Range. Monterey Bay to San Luis Obispo, California. 
Odostomia oldroydi Dali and Bartsch, 1909 
Plate 58, figs. 1, la 
Bulletin 68, United States National Museum, 150; PI. 15, fig. 3. 
Shell elongate-ovate, vitreous. Nuclear whorls small, obliquely im¬ 
mersed in the first of the succeeding turns, above which projects the tilted 
edge which is marked with five raised spiral lirations. Post-nuclear 
whorls somewhat inflated, well-rounded, moderately contracted at the 
sutures, strongly slopingly shouldered at the summit, ornamented with 
somewhat retractive axial ribs, of which fourteen occur upon the first, 
sixteen upon the second, eighteen upon the third, and twenty upon the 
penultimate turn. In addition to the axial ribs, the whorls are marked by 
four spiral cords between the sutures which are as strong as the ribs and 
render them strongly nodulous at their junction. The second of these 
ribs below the summit marks the angle of the shoulder. The spaces 
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