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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 incon- spicuous costae. Color straw to whitish, rarely with brown lines. Uncom- mon from low water to 50 fathoms. This is Scalaria borealis Beck. Genus Opalia H. and A. Adams 1853 Subgenus Demise ala de Boury 1886 Opalia hotessieriana Orbigny Hotessier's Wentletrap Plate 2 2g Southeast Florida and the Caribbean. 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 Plate 20) Forrester Island, Alaska, to off San Diego. 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.