104 



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



Helix ariadnae, Pfr. — Shell with an arcuate rimation, terminathig 

 in a minute oblique perforation, depressed, subdiscoidal, rather solid, 

 nearly transparent, bluish-white, with scarcely perceptible wrinkles on 

 the upper surface ; spire flattened ; whirls five, separated by a distinct 

 suture, flattened, the last one suddenly falling towards 

 Fig. 180. the aperture, very much contracted and pinched behind 

 the peristome, more convex and smoother below ; there is 

 a deeply chiselled, arcuated, umbilical rimation, the um- 

 bilical region is also channelled ; aperture small, ex- 

 tremely complicated with teeth, very oblique. Innately 

 circular, ringent ; peristome white, slightly reflected, its 

 terminations approaching each other and joined by two 

 flexiiose, elevated, acute laminse, converging to a point far 

 within the aperture ; the basal margin of the peristome is 

 Helix ariadncB. also furnished with two stout, entering, converging mar- 

 ginal folds, the right margin of the peristome has a more 

 delicate, deeply seated, elongated lamina, running almost parallel with 

 the peristome. Greater diam. 12, lesser 10 ; height 5 mill. 



Helix ariadnce, Pfeiffer in Zeitsch. f. Mai. 1848, 120; Mon. Hel. Viv. 

 Ill, 266 ; in Chemnitz, ed. 2, I, 372, pi. Ixv, f, 19-21 (1846).— W. 

 G. BiNNEY, Terr. Moll. IV, 76, pi. Ixxviii, f. 1, 3, 4. 

 Helix couchiana, Lea, Proc. Acad. Nat. Sci. Philad. 1857, 102 ; Journ. — ; 



Obs. XI, 139, pi. xxiv, f. 112. 

 Dadalochila ariadna, Tkyon, Am. Journ. Conch. Ill, 66, pi. x, f. 15, 16, 

 18 (1867). 



In the resjion of the Rio Grande, both in Texas and Tamaulipas. 



Helix septeiJlYOlva, Say. — Shell broadly nmbilicated, subeari- 

 nated, discoidal, russet horn-color, with stont 

 striae above, smooth below ; plane above with 

 seven (sometimes eight and a half) or less flat- 

 tened whirls ; equally plane below, with three 

 and a half full, more convex whirls on a level, 

 then ending in a deep, pervious umbilicus, the 

 penultimate somewhat overlapped by the last, 

 the antepenultimate much the largest ; aperture 

 very oblique, remote from the axis, subreniform, 

 constricted behind the peristome ; peristome 

 thickened, bluntly reflected, continuous, its ter- 

 minations joined by an elevated, heavy, tooth- 

 like triangular fold. Greater diam. 15, lesser 13 ; 

 height 4 mill. 



Helix sepfemvolva, 

 enlarged. 



