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162 Avierican Seashells
I to 1/4 inches in length, rather slender, with a quite deep suture, thus
giving the whorls a shouldered appearance. No umbilicus. Color a uniform,
chalky grayish white. Outer lip with a thickened varix. Whorls with numer-
ous groups of foliated costae. Surface pitted with small holes when the
costae or ribs are closely crowded. Uncommon from i8 to 75 fathoms.
C. arcella Rehder is believed to be the young of this species.
Genus Actrsa Morch 1857
Acirsa costulata Mighels and Adams Costate Wentletrap
Arctic Ocean to Massachusetts.
% to 1% inches in length, rather turreted in shape and fairly thin in
structure. 8 to 9 moderately convex whorls are devoid of sculpture except
for weak, incised spiral lines and, in the early whorls, numerous but inconspicuous
costae. Color straw to whitish, rarely with brown lines. Uncommon
from low water to 50 fathoms. This is Scalaria borealis Beck.
Genus Opalia H. and A. Adams 1853
Subgenus Demiseala de Boury 1886
Opalia hotessieriana Orbigny Hotessier's Wentletrap
Southeast Florida and the Caribbean.
Plate 2 2g
H to /4 inch in length, moderately slender. Characterized by 10 to 14
large, square notches along the suture of each whorl. Ribs are rather weak.
Surface, in fresh specimens, microscopically pitted. Color grayish white.
Not uncommon from low water to 90 fathoms. O. crenata Linne (same
range, but also the Eastern Atlantic) is larger, its whorls more strongly
shouldered, and the notches at the suture are much weaker and more nu-
merous.
Opalia UDrobleiDskii Morch Wroblewski's Wentletrap
Forrester Island, Alaska, to off San Diego.
Plate 20)
I to I M inches in length, slender, heavy; looks beachworn; grayish white
in color, often stained purple from the animal's dye gland. With 6 to 8 low,
pronounced, axial, wide ribs. Base of shell bounded by a strong, smooth,
low, spiral cord. Fairly common. O. chacei (Chace's Wentletrap) is probably
a southern representative of this species.
Opalia insculpta Carpenter Scallop-edged Wentletrap
Southern California to west Mexico.