96 



LAND AND FRESH-WATER SHELLS OF N. A. [PART I. 



junction with the body whirl ; on the parietal wall of the aperture is a 

 white fold, hardly connecting the extremities of the peristome, and pro- 

 jecting across the aperture into an acute point ; an internal transverse 

 tubercle on the base of the shell. Greater diam. 11, lesser 9 ; height 

 4 mill. 



Helix tholus, W. G. Binney, Proc. Acad. Nat. Sci. Philad. 1857, 186 ; Terr. 

 Moll. IV, 81, pi. Ixxvii, f. 21.— Pfeiffek, Mon, Helic. Viv. IV, 351. 



Dcedalochila tholus, Tkyon, Am. Journ. Conch. Ill, 64, pi. x, f. 7, 9 (1867). 



Washington Co., Texas. 



The specimens from which the descriptions of H. mooreana 

 and H. tholus were drawn are widely different, but a study of a 

 large suite of individuals leads to doubt their specific distinction, 



Fig. 172. 



Helix liippocrepis, PFEiPFEn. — Shell rimately perforated, de- 

 ])ressed, rather heavy, closely striated, opaque, smoky ; ypire flattened ; 

 suture impressed ; whirls five and a half, narrow, scar, ely convex, the last 

 subcarinated above, more convex below, falling abruptly 

 at the apeiture, and behind it very much contracted and 

 with a prominent isolated bulge ; umbilicus at first ex- 

 panded and grooved, but rapidly terminating in a minute 

 perforation ; aperture almost horizontal, ear-shaped, ring- 

 ent, 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 con- 

 necting terminations of which within the shell resemble a 

 horseshoe ; the upper portion 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 

 diam. 12, lesser 10; height 5 mill. 



Belix filppocrepis, Pfeiffer in Roemer's Texas, 455 (1849) ; in Zoitsch. 



f. Mai. 1848, 119; Mon. Hel. Viv. Ill, 267; in Chkmnitz, ed. 2, II, 



333, pi. cxxxi, f. 4-6.— Reeve, Con. Icon. no. 1238 (1854).— W. G. 



Binney, Terr. Moll. IV, 77, pi. ixxviii, f. 19. 

 Dwdalochila (?) hippocrepis, Tryon, Am. Journ. Conch. Ill, 68, pi. x, f. 



42 (1867). 



New Braunfels, Texas. 



