CLASS GASTROPODA 
17 
pressis; basi subito rotundata, haud umbilicata; apertura subrotundata; 
labropostice parum contracto. Long., 0.06; long, spir., 0.04; lat., 0.02. 
(Carpenter.) 
Type in United States National Museum, No. 15566. Type locality, 
San Pedro, California. 
Shell small, elongate-conic, white. Nuclear whorls minute, apparently 
not differentiated from the remaining turns. Postnuclear whorls strongly 
flattened, somewhat overhanging, separated by a deeply channeled suture, 
apparently without sculpture. Periphery and base of last whorl well 
rounded. Aperture ovate, posterior angle acute, outer lip thin; columella 
short, moderately strong, slightly reflected. (Bartsch.) 
Genus BITTIUM (Leach) Gray, 1847 
Shell elevated, with numerous granular whorls and irregular varices; 
anterior canal short, not recurved; inner lip simple, outer lip not reflected, 
usually with an exterior rib. Operculum four-whorled with central nu¬ 
cleus. (Tryon, Manual of Conchology.) 
Type. Cerithium reticulatum Da Costa. 
Distribution. Europe, Canary Island, Azores, West Indies, New 
England to Florida, Sitka, Alaska, to Monterey, San Pedro, San Diego, 
Australia, Japan, China, New Zealand, Plawaiian Islands. 
Subgenus Bittium s.s. 
Bittium johnstonae Bartsch, 1911 
Proceedings of the United States National Museum, 40:387; PI. 53, fig. 6. 
Shell very elongate-conic, chestnut brown with strong white varices at 
irregular intervals. (Nuclear whorls decollated.) Post-nuclear whorls 
well-rounded, the early turns ornamented with four spiral keels, all of 
which except the anterior one, which is at the summit, are of equal size 
and about as wide as the spaces that separate them; the one at the summit 
being much more slender. On the last three whorls the keel at the summit 
is divided into two slender threads, which occupy the same amount of 
space as the single keel does on the earlier turns. In addition to the spiral 
keels, the whorls are marked by strong, well-rounded, axial ribs which are 
about two-thirds as wide as the spaces that separate them. These ribs 
render the spiral keels tuberculate at their intersection. There are 12 ribs 
upon the third, 14 upon the fourth, 16 upon the fifth and sixth, and 18 
upon the seventh turn. On the last two whorls, four axial ribs occur 
between each pair of varices. Varices very large and conspicuous. Sutures 
strongly constricted. Periphery of the last whorl well-rounded, marked by 
[ 619 ] 
