168 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
between them are roundish pits. Sutures moderately constricted. Periphery 
of the last whorl well-rounded, marked by a cord equaling the one posterior 
to it in width, and separated from that by a line as wide as those on the 
spire. Base moderately prolonged, well-rounded, marked with twelve, 
low, rounded spiral cords, which decrease successively in width from the 
periphery, anteriorly; the spaces separating these cords are also narrow 
impressed lines. Aperture moderately large, oval; posterior angle acute; 
outer lip strongly curved, showing the external sculpture within; inner 
lip slightly curved, oblique, reflected over and adnate to the base, provided 
with a slender fold at its insertion. Parietal wall covered by a thin callus. 
Length, 2; diameter, 1 mm. (Bartsch.) 
Type in United States National Museum, No. 249903. Type locality, 
Coronado Island, San Diego. 
Range. Known only from type locality. 
Odostomia trachis Dali and Bartsch, 1909 
Plate 58, figs. 4, 4a- 
Bulletin 68, United States National Museum, 148; PI. 15, figs. 4, 4a. 
Shell small, elongate-conic. Nuclear whorls small, smooth, strongly 
obliquely immersed in the first of the succeeding turns, above which only 
the tilted edge of the last volution projects. Post-nuclear whorls moder¬ 
ately rounded, strongly contracted at the sutures, slopingly shouldered at 
the summit, marked by strong, rounded, decidedly retractive axial ribs, 
of which sixteen occur upon the second, eighteen upon the third, and 
twenty upon the penultimate turn. In addition to the axial ribs the whorls 
are crossed between the sutures by four spiral cords which are as strong 
as the ribs and render them nodulous at the junction. The second of these 
cords below the summit marks the angle of the shoulder. The spaces 
inclosed by the ribs and cords are deep, squarish pits. Sutures sub¬ 
channeled. Periphery of the last whorl marked by a groove, crossed by 
the spiral ribs, which terminate at the extremity of the first basal cord. 
Base well-rounded, marked by four subequal, distantly spaced, narrow, 
spiral cords, the broad spaces between which are crossed by numerous 
axial threads. Aperture oval; posterior angle obtuse; outer lip thin, show¬ 
ing the external sculpture within; columella slender, reflected, re-enforced 
by the base, provided with a fold at its insertion; parietal wall covered 
with a thin callus. Length, 2.5; diameter, 1 mm. (Dali and Bartsch.) 
Type in United States National Museum, No. 168619. Type locality, 
San Pedro, California. 
Range. Monterey to San Diego, California. 
[466 ] 
