272 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



outer one stron<;ly carinatecl 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 

 of a lens ; aperture rounded, contracted by three teeth ; 

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

 basal extremity, ([uite 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. Mooreana, . /• i 



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



peristome ; an internal transverse tubercle on the base of 

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



Helix Mooreana, ^Y. G. Binney, rroc. Acad. Nat. Sci. Thilad., 1857, 184 ; Terr. 



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



and Ckosse, Moll. Mex. etGuat., 275 (1870). — Pfeiffer, Mon. Hel. Viv., IV. 52. 

 Da^dalochila Mooreana, Tuyox, Am. Journ. Conch., 111. 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. e. 95. — Pfeiffer, 



Mon. Hel. Viv., IV. 351. 

 Dcedalochila thohis, Tuyon, Am. Journ. Conch., III. 64 (1867). 



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

 neiiihborinjj 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 



Fig. 171. 



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 urn- 



