220 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
complete by the thick callus on the parietal wall. Altitude, 0.6; diameter, 
1.2 mm. (Bartsch.) 
Type in United States National Museum, No. 340813. Type locality, 
Whites Point, California. 
Range. California. 
Genus CYCLOSTREMA Marryatt, 1818 
Shell orbicular, depressed, widely umbilicated, spire short; whorls 
transversely striated or cancellated; aperture round, not nacreous; peris¬ 
tome continuous, simple. (Tryon, Structural and Systematic Conchology.) 
Type, C. cancellata, Marryatt. 
Distribution. Cape, India, Philippines, Australia, Peru, California, 
Washington. 
Cyclostrema diegensis Bartsch, 1907 
Plate 107, figs. 7, 8, 9 
Proceedings of the United States National Museum, 32:172; fig. 7. 
Shell exceedingly small, thin planorboid, with a prominent, compressed 
peripheral keel, translucent, yellow horn-colored. Nepionic whorls V/ 2 , 
moderately rounded, not elevated, smooth. The succeeding turns have their 
highest elevation at about one-third of the distance from the suture to the 
periphery, at which place they are raised into a broad, well-rounded ridge 
from which they slope abruptly, convexly rounded, to the suture and 
more gently concavely to the angulated periphery. On the upper surface 
the whorls are ornamented with slender, regularly spaced, oblique riblets, 
which are best developed on the elevated ridge, where they are about one- 
fourth as wide as the spaces that separate them. Sutures strongly marked. 
Periphery with a compressed, obtuse angle. Base moderately rounded, 
broadly, openly umbilicated, with a slender thread, bounding the outer edge 
of the umbilicus and a slender spiral cord situated about halfway between 
the umbilical thread and the periphery. The riblets seen on the upper sur¬ 
face extend feebly beyond the peripheral keel to the first basal cord but 
are reduced to simple incremental lines between this and the umbilical 
thread; columellar wall well-rounded, marked by incremental lines only. 
Aperture oblique, irregularly pentagonal, one blunt angle being formed by 
the elevated part of the whorl, another equally obtuse one by the periphery, 
the third by the basal keel, the fourth by the umbilical angle, and the fifth 
by the junction of the columella with the parietal wall. Outer lip thin, 
showing the sculpture of the shell within. Columella straight and very 
obliquely placed. Parietal wall covered by a thin callus. Greater diameter, 
1.0; lesser diameter, 0.8; altitude, 0.25 mm. (Bartsch.) 
[822 ] 
