. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. POLYGYRA. 273 bilicus, broad at the commencement, and rapidly narrowing beyond the second whorl with the peculiar groove visible in all the whorls of the umbilicus, of the same character as that noticed by Say in auriculata, though deeper. The name tholux is derived from the resemblance of the slightly raised, rounded spire to a low dome. Jaw with about 15, adjoining, broad ribs, denticulating either margin. The lingual membrane of Mooreana (PI. VI. Fig. Q) has 20—1—20 teeth, with 8 laterals. There are two transition
. Bulletin of the Museum of Comparative Zoology at Harvard College. Zoology. POLYGYRA. 273 bilicus, broad at the commencement, and rapidly narrowing beyond the second whorl with the peculiar groove visible in all the whorls of the umbilicus, of the same character as that noticed by Say in auriculata, though deeper. The name tholux is derived from the resemblance of the slightly raised, rounded spire to a low dome. Jaw with about 15, adjoining, broad ribs, denticulating either margin. The lingual membrane of Mooreana (PI. VI. Fig. Q) has 20—1—20 teeth, with 8 laterals. There are two transition teeth with simple inner cutting point. Genitalia not examined. Polygyra hippocrepis, Pfeiffer. Shell rimately perforated, depressed, rather heavy, closely striated, opaque, smoky; spire flattened; suture-impressed; whorls b\, narrow, scarcely con- vex, the last subcarinated above, more convex below, fall- ing abruptly at the aperture, and behind it very much con- tracted and with a prominent isolated bulge; umbilicus at first expanded and grooved, but rapidly terminating in a mi- nute perforation ; aperture almost horizontal, ear-shaped, rin- gent, complicated with teeth; peristome white, thickened, its extremities joined by an elevated, sharp, angular ridge, from which protrude far within the aperture two laminae (the upper one sharper and more prominent), the connecting terminations of which within the shell resemble a horseshoe; the upper por- tion of the peristome is slightly reflected and furnished with an oblique entering angle, and the basal portion is callous and reflected; an internal transverse tubercle on the base of the shell. Greater diameter 12, lesser 10 mill.; height, 5 mill. Helix hippocrepis, Pfeiffer in Roemer's Texas, 455 (1849) ; in Zeitsch. fur Mai., 1848, 119 ; Mon. Hel. Viv., III. 267; in Chemnitz, ed. 2, II. 333, PL CXXXI. Figs. 4 - 6. — Reeve, Con. Icon., No. 1238 (1854). — W. G. Binney, Terr. Moll., IV. 77, PI. LXXVIII. Fig. 19 ; L. &
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