with a concave lamella and two tubercular teeth, the parietal wall bearing a low, thin lamella with a short, V-shaped hook.
Description of type.—Shell depressed, spire low, periphery slightly shouldered near the suture, base convex; perforately and narrowly umbilicated, the umbilicus rapidly enlarging at the last whorl to about one-third of the diameter of the shell. Surface light-colored, densely, regularly, and finely ribbed, the ribs vanishing toward the umbilicus; no spirals between the ribs. Whorls 6¾, rather convex, regularly growing, the periphery at the shoulder above the middle; the last whorl abruptly descending near the aperture, deeply and narrowly constricted behind the lip.
Fig. 12. Polygyra (Erymodon) hertleini, new sp. CNHM No. 106703, type; views from above, below, and side; about × 2.
Aperture oblique, crescent-shaped, thinly lipped. Outer lip narrowly expanded, bearing a concave lamella with a denticle at its lower end; basal lip with a marginal, round denticle. Parietal wall bearing a lamella with a hardly visible hook-like appendix at its inner end.
Measurements: Diameter, 13.2 mm.; height, 6.3 mm.; diameter of aperture, 4.5 mm.; height of aperture, 4.0 mm.; diameter of unbilicus, 3.5 mm.
Type.—Chicago Natural History Museum No. 106703. Collected on Tenecatita Bay, Jalisco, Mexico, about 1½-2 miles up trail, by Leo G. Hertlein, February 15, 1932.
Additional material.—Four more specimens with the same data as the type are at hand. One of these paratypes is Chicago Natural History Museum No. 106704, and three are in the California Academy of Sciences in San Francisco, No. 27212. All these specimens agree perfectly with the type, differing slightly only in the measurements: diameter, 13.2-14.0 mm.; height, 6.6-7.3 mm.
Relationships.—There can be no doubt that this new species has its closest relative in Polygyra (Erymodon) matermontana Pilsbry. My friend and colleague, Dr. Alan Solem, was kind enough to compare my new species with the specimens of Pilsbry's species matermontana in the Philadelphia Academy of Sciences, and he
