272 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



outer one strongly carinated so as to conceal a portion of the umbilicus and a 

 great part of the remaining whorl ; the umbilicus is very small, but perforates 

 the shell to the apex, showing all the volutions with the aid 

 Fig. 170. of a lens ; aperture rounded, contracted by three teeth ; 



peristome heavy, broad, white, hardly reflected, near the 

 basal extremity, quite on the edge, armed with two short, 

 incurving teeth, separated by a small, rounded sinus ; on 

 the columella there is a tooth-like fold, square, projecting 



P. Moor -e ana, . . . , , 



enlarged. across the aperture, its extremities joining those of the 



peristome ; an internal transverse tubercle on the base of 

 the shell. Greater diameter 8J, lesser 7 mill. ; height, 3 mill. 



Helix Mooreana, W. G. BINXEY, Proc. Acad. Nat. Sci. Philad., 1857, 184; Terr. 



Moll., IV. 80, PL LXXVIII. Fig. 24 ; L. & Fr.-W. Sh., I. 95 (1869). FISCHER 



and CROSSE, Moll. Mex. et Guat., 275 (1870). PFEIFFER, Mon. Hel. Viv., IV. 52. 

 Dccdalochila Mooreana, TRYON, Am. Journ. Conch., III. 64 (1867). 

 Helix tholus, W. G. BINNEY, Pioc. Acad. Nat. Sci. Philad., 1857, 186 ; Terr. 



Moll., IV. 81, PI. LXXVII. Fig. 21 ; L. & Fr.-W. Sh., 1. c. 95. PFEIFFER, 



Mon. Hel. Viv., IV. 351. 

 Dcedalochila tholus, TRYON, Am. Journ. Conch., III. 64 (1867). 



Texan Subregion, Washington and Bosque County, Texas ; also in the 

 neighboring Mexican States. 



The specimens from which the descriptions of Mooreana and tholus were 

 drawn are widely different, but a study of a large suite of individuals leads one 

 to doubt their specific distinction. Although I now refer P. tholus to Mooreana, 

 I here repeat the original description and figure. 



Shell broadly umbilicated, depressed-globose, rather solid, white, shining, 

 ribbed above, smoother below ; spire obtuse, little elevated, rounded ; whorls 7, 

 convex, the upper ones more flattened, the last bluntly 

 carinated; carina not reaching the peristome; base parallel 

 to the suture ; umbilicus broad, half the larger diameter of 

 the shell, showing two and a half deeply grooved whorls 

 plainly, the others rapidly retreating towards the apex ; aper- 

 ture very oblique, semicircular, removed from the axis of the 

 shell, bordered with a scarcely reflected, white, heavy peri- 

 stome, grooved behind, and armed with two stout teeth near 

 the basal extremity, broadly reflected at the junction with 

 the body whorl ; on the parietal wall of the aperture is a 

 white fold, hardly connecting the extremities of the peri- Helix tholus, 

 stome, and projecting across the aperture into an acute point ; 

 an internal transverse tubercle on the base of the shell. Greater diameter 1 1 , 

 lesser 9 mill. ; height, 4 mill. 



The aperture of this curious shell (tholus) resembles that of P. fatigiata, Say. 

 It is readily distinguished from that and all other described species by the um- 



