224 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
turns increasing regularly in size like Planorbis, rendering the apex con¬ 
siderably lower than any of the succeeding turns, the last being the most 
elevated. Whorls well-rounded, separated by strongly impressed sutures 
and marked by many equally strong and equally spaced, somewhat wavy, 
incised spiral lines and the fine incremental lines. At more or less regular 
intervals there appear slight constrictions which coincide with the lines 
of growth. Periphery of the last whorl well-rounded. Base well-rounded, 
very broadly and openly umbilicate to the very apex, marked like the upper 
surface. Aperture oblique, suboval; outer lip thin; columella short, form¬ 
ing almost a straight line with the faint callus of the parietal wall. The 
type has a little more than three and a half whorls and measures: greater 
diameter, 2.3; lesser diameter, 1.8; altitude, 0.8 mm. (Bartsch.) 
Type in United States National Museum, No. 125537. Type locality, 
Long Beach, California. 
Range. San Pedro to San Diego, California. Fossil: Pleistocene. 
Cyclostremella concordia Bartsch, 1920 
Journal of the Washington Academy of Sciences, 10:1920. 
Shell very small, planorboid, hyaline, semitransparent. Early whorls 
eroded in all the specimens seen. The last two whorls curve suddenly to 
the deeply channeled suture on the upper surface; the rest gradually, 
evenly rounded. Periphery of the last whorl well-rounded. Base openly 
umbilicated. The entire surface of spire and base is marked by rather 
strong, irregularly developed incremental lines and more or less equal and 
equally spaced fine spiral lirations. The intersections of these two sculp¬ 
tured elements give to the surface of the shell the characteristic beaded 
sculpture of the genus. Aperture very broadly ovate, almost subcircular, 
the narrower position being at the posterior angle; peristome thin, not 
reflected ; parietal wall covered by a thin callus. Operculum thin, corneous, 
paucispiral. Altitude, 1 ; diameter, 2 mm. (Bartsch.) 
Type in United States National Museum, No. 340862. Type locality, 
Olga, Orcus Island, Washington. 
Range. Known only from type locality. 
Genus SCISSILABRA Bartsch, 1907 
Vitrinella -like shells with the middle of the outer lip deeply and broadly 
notched, the center of the notch coinciding with the periphery of the shell. 
(Bartsch.) 
Type. Scissilabra dalli. 
Distribution. California to Gulf of California. 
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