Page:American Seashells (1954).djvu/189

Rh $1/3$ inch in diameter, strong, opaque-white, depressed, 4 whorls. Top of whorls rounded, slightly concave just below the fine suture; bearing 5 or 6 major, smooth, spiral threads on top with numerous, much finer threads between. Periphery bordered above and below by a major cord. Umbilicus widely funnel-shaped, deep. Outer lip crenulate above. Not uncommon in shallow water. One of our largest American Vitrinellid species. Provisionally placed in this subgenus.

$3/8$ inch in diameter, dull-white, planorboid, with a very flat spire and a wide concave, non-umbilicate base. Periphery of shell flat, bordered above and below by one or two spiral cords of small beads. Aperture squarish. Operculum round, multispiral with a chitinous pimple on the inside. A rare and choice collector’s item. Deep water. 70 fathoms.

1.8 mm. in diameter, 3 to 4 whorls, semitranslucent-white to burnt sienna. Sculpture of fine, spiral striae and strong, widely spaced, radial ribs. Peripheral zone flattened or concave between 2 projecting nodulose keels. Under rocks. Moderately common to rare. This genus was formerly placed in the family Architectonicidae.

Shells usually about 2 to 3 mm. in diameter, depressed, glossy, white, usually smooth, and with an umbilical callus. They are very distinctive little shells, but require a high-powered lens for their inspection. We have figured only one species, but have included a key from the work of Pilsbry and McGinty (1945) (see pl. 17y).