CLASS GASTROPODA 
251 
surface of the spire is crossed by numerous microscopic spiral lines and 
lines of growth. Periphery of the last whorl ornamented by a tubercular 
keel, which is not quite as strong as the supraperipheral keel. Base dark 
brown, moderately long, marked by two strong spiral keels, the anterior 
one of which is situated partly upon the columella, while the other one 
occupies a plane halfway between the anterior and the peripheral keel. 
Ihe spaces which separate these keels are about equal in width and are 
crossed by slender continuations of the axial riblets. Columella stout and 
twisted, marked by slender spiral lirations. Aperture pyriform, strongly 
channeled anteriorly and posteriorly; outer lip patulous, marked within 
by a light brown band posteriorly and a narrow dark-brown zone at the 
base; columella and parietal wall covered with a thick callus. Length, 5.1; 
diameter, 1.9 mm. (Bartsch.) 
Type in United States National Museum, No. 152206. Type locality, 
San Pedro, California. 
Range. San Pedro, California, to South Coronado Island. Fossil, 
Upper San Pedro Series, at the lumber yard, San Pedro, California. 
Trifora montereyensis Bartsch, 1907 
Plate 71, fig. 17 
Proceedings of the United States National Museum, 33:249; PI. 16. fig. 17. 
Shell rather stout, brown, with a wax-yellow band about one-third the 
width of the height of the whorls encircling the middle of the turns. 
(Nucleus decollated in all the specimens examined.) Post-nuclear whorls 
separated by strongly channeled sutures, ornamented on the early turns 
by a double spiral row of tubercles and on the last three by a triple row, 
the median one of which is very slender on all but the last turn and is 
situated a little nearer the posterior row than the suprasutural one. There 
are twenty tubercles upon the second and twenty-six upon the penultimate 
turn. These tubercles are joined by moderately strong spiral bands and 
axial riblets which inclose strongly impressed rounded pits between them. 
The periphery is marked by a keel almost as strong as the supraperipheral 
one, while the base, which is uniformly dark brown, bears two prominent 
keels, the anterior one of which is well upon the short, stout columella. 
The channels between these keels are crossed by the feeble extensions of 
the axial riblets. Aperture strongly channeled anteriorly and posteriorly; 
columella and parietal wall covered with a strong callus. The type has 
the last seven whorls and measures: Length, 4.6; diameter, 2.2 mm. 
(Bartsch.) 
Type in United States National Museum, No. 32216. Type locality, 
Monterey, California. 
Range. Known only from the type locality. 
[ 549 ] 
