. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. POLYGYRA. 275 same purpose in the economy of the animal, as the " fulcrum "originally noticed by Mr. Li-a (Observations, Vol. V. p. 80) in Slrenotrema spinosutriy though of a difl'oivnt construction. Jaw slightly arcuate, long, low, with about 20 ribs on the anterior surface, crcnulatiug either margin. P. /asti< (IM. VI. Fig. II) has 21—1—21 teeth, with 8 laterals on the linorual membrane. Polygyra Jacksoni, Bland. Shell narrowly umbilicate, depressed, shining, dark or pale horn-colored, li
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology; Zoology. POLYGYRA. 275 same purpose in the economy of the animal, as the " fulcrum "originally noticed by Mr. Li-a (Observations, Vol. V. p. 80) in Slrenotrema spinosutriy though of a difl'oivnt construction. Jaw slightly arcuate, long, low, with about 20 ribs on the anterior surface, crcnulatiug either margin. P. /asti< (IM. VI. Fig. II) has 21—1—21 teeth, with 8 laterals on the linorual membrane. Polygyra Jacksoni, Bland. Shell narrowly umbilicate, depressed, shining, dark or pale horn-colored, little elevated above, striated, convex beneath, with finer almost obsolete striae; whorls 6, slightly convex, gradually increasing, the last sud- denly deflected, contracted and above gibbously inflated behind the aperture; suture impressed; aperture oblique, lunate- circular, with 3 teeth; peristome thickened, brownish-red, shortly reflected, with the scarcely approaching margins joined by a white, linguiform, bicrural, deeply entering tooth, the basal margin with a strong, oblique, sinuous fold, the right with a deeply seated mill.: heiuht, 4 mill. tooth. Greater diameter 7, lesser 6. p. Jacksoni. Helix Jacksoni, Bland, Am. Journ. Conch., II. 371, PI. XXI. Fig. 8 (1866).— W. G. BiNNEY, L. & Sh., I. 98, Fig. 174 (1869). Dcedalocliila Jacksoni, Tryon, Am. Journ. Conch., III. 67 (1867). Fort Gibson, Indian (Cherokee) Territory; Springfield, Mo. I am inclined to rank it among the species of the Texan Subregion. This species belongs to the same group as, and is most nearly allied to, P. Hazardi, Bland (P. plicata, Say), from which, however, it may be readily dis- tinguished by the very different character of the parietal and basal teeth. Tliis species has no internal tubercle. Animal not observed. Fig. 175. Polygyra Troostiana, Lea. Shell riraately umbilicated, discoidal, slightly convex above, flat- tened below, obtusely carinated, with separated strong- rib-like
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