CLASS GASTROPODA 
225 
Scissilabra dalli Bartsch, 1907 
Plate 104, figs. 10, 11, 12; Plate 107, figs. 10, 11, 12 
Proceedings of the United States National Museum, 32:176; fig. 11. 
Shell small, depressed, lenticular, with acutely angulated periphery, 
having 3J/2 transparent, vitreous whorls which are separated by well- 
marked sutures. The nepionic portion consists of the first \ 2 /$ turns and 
is scarcely differentiated from the rest of the shell. The upper surface 
is evenly and gently rounded from the summit to the periphery, which is 
strongly and sharply carinated. Under side openly umbilicated, much less 
convex than the upper. The umbilical edge is marked by an acute carina 
from which the columellar wall in the last whorl extends almost vertically 
to where it joins the preceding turn. This carina and vertical umbilical 
wall are characteristic of the last turn only; in all the others which are 
visible in the umbilicus it appears evenly rounded. Aperture very large, 
decidedly oblique; outer lip very broadly and strongly notched, the blunt 
angle of the notch coinciding with the periphery of the shell; the portion 
of the lip posterior to the sinus and its basal part somewhat sinuous; 
columella vertical and slightly concave; parietal wall covered by a thick 
callus which renders the peritreme almost continuous. Greater diameter, 
2; lesser diameter, 1.5; altitude, 0.75 mm. (Bartsch.) 
Type in United States National Museum, No. 192712. Type locality, 
San Diego, California. 
Range. Monterey, California, to Gulf of California. 
Genus LEPTOGYRA Bush, 1897 
Shell minute, semitransparent, dull, dirty white or faintly brown shells 
covered with a thin, rather tough, delicate straw-colored epidermis, con¬ 
sisting of a few convex whorls forming an elevated spire with relatively 
large, smooth, slightly twisted nuclear whorl and large body-whorl. Suture 
deep, somewhat channeled. Umbilicus relatively large, round, deep, show¬ 
ing .some of the whorls, with well-rounded walls. Aperture very oblique, 
somewhat ovate. Periostome simple, continuous, modified on the body- 
whorl into a thin glaze, sometimes in the adult having a free edge; strongly 
sinuate along the umbilical region and anteriorly, slightly angulated below, 
at the junction of the two lips; above arching well upward, forward, then 
backward, from the body-whorl, forming a distinct sutural notch. Interior 
of the aperture smooth and very lustrous, with the conspicuous, exterior 
transverse lines showing through by transparency. There is no opaque 
internal line; in all the specimens the operculum is drawn well into the 
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