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 tholus 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 (PL VI. Fig. Q) has 20120 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 5^, 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 uppef 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. fiir 

 Mai., 1848, 119 ; Mon. Hel. Viv., III. 267 ; in CHEMNITZ, ed. 2, II. 333, PI. 

 CXXXI. Figs. 4 - 6. REEVE, Con. Icon., No. 1238 (1854). W. G. BINNEY, 

 Terr. Moll., IV. 77, PI. LXXVIII. Fig. 19 ; L. & Fr.-W. Sh. I. 96, Fig. 172 

 (1869). 



Dcedalochila (?) hijipocrcpis, TRYON, Am. Jouru. Conch., III. 68 (1867). 



Texan Subregion, at New Braunfcls, Texas. 

 Animal not observed. 



Polygyra fastigans, L. W. SAY. 



Shell rimately perforated, plane above, inflated below, with fold-like 

 striae above, smoother below, somewhat shining, of a russet horn-color, hir- 

 sute; spire flattened; whorls 6i, flattened, the last acutely carinated above, 

 very abruptly deflected at the aperture, scrobiculated, constricted, convex 

 below; aperture very oblique, subreniforni, very much contracted, triden- 



VOL. IV. 18 



