176 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
the median keel. The deep channels between the keels and the shoulders 
are crossed by slender axial riblets which have a protractive slant on the 
shoulder and are decidedly retractive in the channels. Periphery of the 
last whorl marked by a keel a little weaker than those between the 
sutures. Base short, well-rounded, narrowly umbilicated, marked by three 
spiral cords and a slender, raised thread about the umbilicus, the channels 
bounding the peripheral cord and those of the base are crossed by riblets 
as on the spire. Aperture large; posterior angle obtuse; outer lip rendered 
angulated by the keels, thus showing the external sculpture within; 
columella slender, very strongly curved, slightly reflected, provided with a 
weak fold at its insertion ; parietal wall covered with a weak callus. Length, 
2.5; diameter, 1 mm. (Dali and Bartsch.) 
Type in United States National Museum, No. 106501. Type locality, 
Point Abreojos, Lower California. 
Range. San Pedro, California, to Point Abreojos, Lower California. 
Subgenus Menestho Moller, 1842 
Odostomia amilda Dali and Bartsch, 1909 
Bulletin 68, United States National Museum, 187; PI. 21, fig. 4. 
Shell ovate, transparent. Nuclear whorls deeply obliquely immersed 
in the first of the succeeding turns, above which only the tilted edge of 
the last whorl projects. Post-nuclear whorls well-rounded, slightly con¬ 
tracted at the sutures, and somewhat shouldered at the summits, the first 
marked by four, slender, equal and subequally spaced, incised, spiral lines; 
the rest are marked by a strongly incised groove a little below the summit, 
which causes this to appear bounded by a well-rounded cord; the remainder 
of the whorls between the sutures show a few distantly spaced and feebly 
incised, spiral lines and numerous very fine, decidedly retractive lines of 
growth. Periphery of the last whorl well-rounded. Base somewhat in¬ 
flated, well-rounded, slightly attenuated anteriorly, marked by numerous 
exceedingly fine, microscopic spiral striations and three, well-incised, equal 
and equally spaced lines on the anterior half. Aperture oval, somewhat 
effuse anteriorly; posterior angle obtuse; outer lip thin, showing the 
external sculpture within; columella slender, decidedly curved, somewhat 
reflected, re-enforced by the base; provided with a strong fold at its 
insertion. Length, 2.6; diameter, 1.3 mm. (Dali and Bartsch.) 
Type in United States National Museum, No. 206907. Type locality. 
Round Island, Lower California. 
Range. San Diego, California, to Round Island, Lower California. 
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