28 
MARINE SHELLS OF WEST COAST OF NORTH AMERICA 
Suture strongly constricted. Periphery of the last whorl rendered angu- 
lated by a cord. Base short, slightly concave, marked by five low, broad, 
well-rounded, obsolete cords, which are subequal and subequally spaced. 
Aperture broadly oval, rather strongly channeled anteriorly; posterior 
angle obtuse; outer lip thin, rendered sinuous at the edge by the external 
sculpture, showing the external markings within; inner lip somewhat sinu¬ 
ous, rather stout, reflected over and appressed to the base; parietal wall 
covered by a moderately thick callus. Length, 13; diameter, 1.2 mm. 
(Bartsch.) 
Type in United States National Museum, No. 272376. Type locality, 
San Juan Island, Washington. 
Range. Known only from type locality. 
Bittium sanjuanensis Bartsch, 1917 
Plate 74, fig. 4 
Proceedings of the United States National Museum, 52:674; PI. 47, fig. 4. 
Shell very large, rather thin, bluish white. Nuclear whorls decollated. 
Post-nuclear whorls almost appressed at the summit, well-rounded, de¬ 
cidedly contracted immediately posterior to the suture, marked by strong, 
broad, heavy, slightly protractive, axial ribs which become enfeebled 
toward the summit and slightly widened there. Of these ribs 12 occur 
upon the second and third, 14 upon the fourth and fifth, and 16 upon the 
last whorl. Intercostal spaces not quite as broad as the ribs. The spiral 
sculpture consists of five cords, of which the first, which is at the summit, 
is very slender. The two succeeding this are successively a trifle stronger, 
while the fourth and fifth are very strong, the last being the heaviest of 
all. The junction of the axial ribs and the spiral cords form well-rounded, 
elongated nodules, which have their long axis parallel with the spiral 
sculpture; the spaces inclosed between them are very shallow, rectangular 
pits. In addition to the above sculpture, the entire surface of the spire and 
base is marked by many very slender lines of growth and exceedingly fine 
microscopic spiral striations, the combination of which gives the surface 
a somewhat cloth-like texture. Suture strongly constricted; it would be 
channeled were it not for the fact that the peripheral keel makes its appear¬ 
ance above the summit of the whorl, hence removes the strongly channeled 
element. Periphery of the last whorl marked by strong spiral cord, which 
is about as far anterior to the fifth cord of the spire as that is separated 
from the fourth. Base very short, decidedly concave, marked by three 
slender spiral cords, of which the first is about as far anterior to the 
periphery as that is distant from the fifth cord on the spire. The other two 
cords are very slender, the first being at the base of the columella while 
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