CLASS GASTROPODA 
171 
Subgenus Ividella Dali and Bartsch, 1909 
Odostomia navisa Dali and Bartsch, 1907 
Plate 57, fig. 2 
Proceedings of the United States National Museum, 33:517; PL 46, figs. 2, 2a. 
Shell of medium size, strongly sculptured, subdiaphanous to milk- 
white. Nuclear whorls at least 2, obliquely a little more than half im¬ 
mersed. Post-nuclear whorls strongly shouldered, subtabulated, with a 
strong, broad, spiral keel limiting the anterior edge of the shoulder and an 
acute raised keel on the middle of the whorls between the sutures, while 
a third equally acute keel marks the periphery of the last whorl. Two 
other keels ornament the base, the anterior one of which is not quite as 
strong as its neighbor. The axial sculpture consists of narrow, more or 
less lamellar, almost vertical ribs, which render the intersection with the 
spiral keels somewhat thickened but not nodulose. These axial ribs extend 
over the periphery and base of the last whorl to the umbilical region, 
gradually growing weaker as they approach this point. There are about 
eighteen on the second and twenty upon the penultimate whorl. The 
spaces between the ribs and keels appear as concave quadrangular depres¬ 
sions. Umbilicus narrowly perforated. Suture deeply channeled by the 
shouldered whorl. Aperture suboval, posterior angle decidedly obtuse; 
outer lip thick, marked by five projections, corresponding to the five keels; 
columella almost straight, strongly revolute with a conspicuous oblique 
fold near its insertion; parietal wall covered by a faint callus showing both 
basal keels, the anterior faint and just posterior to the insertion of the 
columella and the next on the middle of the wall. Length, 2.7; diameter, 
1.3 mm. (Dali and Bartsch.) 
Type in United States National Museum, No. 106502. Type locality, 
Scammons Lagoon, Lower California. 
Range. San Pedro, California, to Scammons Lagoon, Lower Cali¬ 
fornia. 
Odostomia navisa delmontensis Dali and Bartsch, 1907 
Plate 57, figs. 3, 3 a 
Proceedings of the United States National Museum, 33:518; PI. 46, figs. 3, 3a. 
Shell similar to O. mvisa but more elongate, and in every way more 
delicate, with lamellose sculpture reduced almost to raised cords and with 
stronger shouldered summits and more open umbilicus. Length, 3.2; 
diameter, 1.3 mm. (Dali and Bartsch.) 
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