Bulletin - United States National Museum - Smithsonian Institution

104 BULLETIN 91, UNITED STATES NATIONAL MUSEUM.
posterior row of tubercles on each turn flesh colored. Nuclear
whorls 3^, the first half smooth, the remainder marked by two slender
spiral threads, which are placed anterior and posterior to the middle
of the whorls, leaving a narrow space between them about one-half
the width of that between the summit and the first spiral thread
below it. In addition to the spiral threads, these whorls are marked
with slender axial riblets, which curve strongly, retractively from the
summit to the first spiral thread, crossing the space between the two
spiral threads in a straight, retractive line, then continuing over the
anterior portion of the wall in a slightly curved, protractive manner.
These riblets are very feeble on all but the last nuclear whorl, on
which they are much stronger. On this there are 34. Postnuclear
whorls flattened. The first four are marked with two strong spiral
cords, of which one is immediately below the shouldered summit,
while the other is a little above the suture. Beginning with the fifth,
a slender spiral cord makes its appearance half way between the other
two. This increases rapidly in size and on the seventh is equal to
the others. In addition to this spiral structure, the whorls are
marked with strong axial ribs, of which 16 occur upon the first, 18
upon the second to sixth, 20 upon the seventh to ninth, and 22 upon
the penultimate turn. On the first four whorls, the junction of the
axial ribs and spiral cords form strong, rounded tubercles on the cord
at the summit, while at the anterior cord the tubercles are truncated
posteriorly and slope gently anteriorly, the whole having a somewhat
dumbbell shape. On the remaining cords the same structure
applies to the shape of the tubercles of the first and third cords,
while on the median cord of the fourth and fifth whorls the tubercles
are elongate-oval, having their own axes parallel with the spiral
sculpture. On the remaining cords, the tubercles and the median
cords resemble those of the supraperipheral cord. The spaces
inclosed between the spiral cords and the axial ribs are large, well
impressed, squarish pits on the first four turns, while on the remain-
ing turns they appear as rounded pits. Sutures strongly impressed.
Periphery of the last whorl marked by a smooth spiral cord, which is
separated from the supraperipheral cord by a groove about as wide
as that which separates the supraperipheral cord from its posterior
neighbor, and crossed by the continuations of the axial riblets which
terminate at the posterior border of the peripheral keel. Base
moderately long, well rounded, marked by three, strong, broad, low,
rounded, equally spaced, spiral cords, which are separated by narrow,
rounded, impressed channels. The last one of these is partly upon
the columella. Aperture irregular, decidedly channeled anteriorly;
posterior angle obtuse; outer lip rendered sinuous and irregular by
the external sculpture; columella covered with a very thick callus
which is reflected over the base and extends over the parietal wall.