222 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
whorls with a strong, broad, rounded keel at the periphery and another 
almost as strong about one-third of the distance between the periphery and 
the summit, where it forms a decided shoulder. The space between the 
appressed summit and the shoulder is marked by twelve subequal and sub- 
equally spaced, spiral cords, the spaces between which are crossed by very 
slender, retractive, axial threads ; the latter are about one-fourth as wide as 
the spaces which separate them, while the spaces between them are only 
about one-half the width of the spiral cords. The space between the pe¬ 
ripheral keel and the strong shoulder is crossed by nine subequal and sub- 
equally spaced spiral cords, and the continuations of the axial threads. 
Here the spiral sculpture is not quite as strong as on the upper surface and 
the spaces inclosed between the axial riblets and the spiral threads are more 
or less quadrangular pits. Base well-rounded, marked like the upper sur¬ 
face, with the sculpture a little less pronounced. Umbilicus open; parietal 
wall showing ten equal and equally spaced spiral cords, which are as wide 
as the spaces that separate them, the latter being crossed by feeble continu¬ 
ations of the axial riblets. Aperture subcircular; outer lip rendered some¬ 
what angular by the two keels; columella evenly curved. (Bartsch.) 
Type in United States National Museum, No. 214100. Type locality, 
Gulf of California. 
Range. San Pedro, California, to Gulf of California. 
Genus CIRCULUS Jeffreys, 1865 
Coquille subdiscoidale, a peine nacree; ombilic tres large; ouverture 
subquadrangulaire; opercule normal. (Fischer.) 
Type. Circulus striatus, Philippi. 
Distribution. Europe, west coast of America. 
Circulus rossellinus Dali, 1919 
Proceedings of the United States National Museum, 56:368. 
Shell minute, white, solid, depressed turbinate, of two and a half 
whorls, including the smooth nucleus; suture distinct; sculpture of 
numerous close-set spiral threads rather large for the size of the shell, 
crossed by microscopic incremental lines; base rounded, with a narrow 
deep umbilicus; aperture subcircular, the outer lip sharp, much produced 
above, pillar lip thickened, not reflected; height, 0.75; longer diameter, 
2 mm. (Dali.) 
Type in United States National Museum, No. 223286. Type locality, 
off South Coronado Island, near San Diego, California, 3 fathoms. 
Range. San Diego, California. 
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