CLASS GASTROPODA 
163 
inclosed by the ribs and cords are strongly impressed oblong pits, the long 
axis of which coincides with the spiral sculpture. Sutures strongly con¬ 
stricted. Periphery of the last whorl marked by a spiral groove, crossed 
by the continuations of the axial ribs, which terminate at the posterior 
edge of the first basal keel. Base well-rounded posteriorly, somewhat 
attenuated anteriorly, marked by six almost equal spiral keels, which are 
less developed about the umbilical area. The deep grooves between these 
keels are crossed by numerous very slender, raised, axial threads. Aperture 
oval; posterior angle obtuse; outer lip thin, showing the external sculpture 
within; rendered decidedly sinuous by the spiral cords; columella moder¬ 
ately strong, decidedly reflected anteriorly, provided with a fold at its 
insertion. Length, 3.5; diameter, 1.7 mm. (Dali and Bartsch.) 
Type in United States National Museum, No. 162765. dype locality, 
San Diego, California. 
Range. San Pedro, California, to Coronado Islands, Mexico. 
Odostomia oregonensis Dali and Bartsch, 1907 
Plate 59, fig. 3; Plate 57, figs. 10, 10a 
Proceedings of the United States National Museum, 33:516; PI. 46, figs. 10, 10a. 
Shell elongate-conic, slender, subdiaphanous to milk-white. Nuclear 
whorls immersed, the last one only being visible. This is somewhat tilted 
and marked by three, strong, narrow, spiral keels and many slender, raised, 
axial threads which cross the grooves between the keels. Post-nuclear 
whorls well-rounded, slopingly shouldered at the summit and separated 
by constricted sutures, ornamented by almost equal and equally-spaced 
spiral keels and axial ribs between the sutures on the spire. There are 
four spiral keels on the first, second, and third whorls, six on the fourth, 
and seven upon the penultimate whorl. The first of these keels is on the 
shoulder of the whorl near the summit and is somewhat less developed 
than the rest. The axial ribs are best developed on the early whorls, 
where they extend equally strong from the summit to the periphery; on 
the antepenultimate and penultimate turns they become somewhat en¬ 
feebled from the middle of the whorl between the sutures to the periphery. 
There are about sixteen of these ribs on the first, eighteen on the third, 
twenty upon the fourth, and twenty-two upon the penultimate turn. The 
intersections of the ribs and spiral keels form low elongated tubercles, 
the long axis of which coincides with the spiral sculpture. The meshes 
inclosed by the keels and ribs are deeply-impressed squarish pits. Periphery 
and base of the last whorl well-rounded, the latter somewhat inflated and 
marked by six spiral cords which are successively closer spaced and a 
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