160 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
ated anteriorly, marked by seven spiral cords, which grow successively 
weaker from the periphery toward the umbilical region and are separated 
by slender, deeply-incised spiral lines. Aperture large, broadly oval; 
posterior angle acute; outer lip thin, showing the external sculpture within; 
columella moderately strong, curved, reflected, and re-enforced by the 
base; provided with an oblique fold at its insertion. Length, 4.2; diameter, 
2 mm. (Dali and Bartsch.) 
Type in United States National Museum, No. 60905. Type locality, 
San Diego, California. 
Range. San Pedro, California, to Coronado Islands. 
Odostomia heterocincta Bartsch, 1912 
Proceedings of the United States National Museum, 42:274; PI. 36, figs. 4, 4 a. 
Shell moderately large, elongate-conic, with decidedly channeled 
sutures, white. Nuclear whorls at least two, forming a depressed helicoid 
spire, which is obliquely, almost one-half immersed in the first of the 
succeeding turns. Post-nuclear whorls moderately rounded, marked by 
strong, decidedly retractive, axial ribs and, on the first four turns, by 
three spiral cords which equal the ribs in strength; the middle one of 
these three cords is a little nearer that at the summit than to the one 
anterior to it. Of the ribs, sixteen occur upon all the whorls. The inter¬ 
section of the ribs and spiral cords form strong, compressed tubercles, the 
long axes of which coincide with the spiral sculpture. The spaces between 
the cords and ribs are well-rounded, strongly impressed pits. The median 
cord on the first four whorls is a little stronger than the other two. On 
the penultimate whorl a slender, spiral cord makes its appearance between 
the median and the supraperipheral cord, which on the last turn, immedi¬ 
ately behind the aperture, attains a strength equal to that of the spiral 
cord at the summit. Entire surface of the spire marked by numerous, 
very fine, incremental lines. Periphery of the last whorl marked by a 
deep channel across which the axial ribs extend feebly. Base of the last 
whorl well-rounded, marked by four strong spiral keels, which are sub- 
equally spaced and grow somewhat weaker successively from the peri¬ 
pheral to the umbilical area. Immediately anterior to the last of these 
spiral keels there is a single, slender, raised, spiral thread. The spaces 
between the spiral keels are crossed by slender continuations of the axial 
ribs and very fine lines of growth. Aperture oval; outer lip fractured; 
inner lip oblique, strong, slightly reflected upon and adnate to the base, 
provided with a moderately strong fold at its insertion; parietal wall 
glazed with a thin callus. Length, 3.2; diameter, 1.3 mm. (Bartsch.) 
[ 458 ] 
