280 . TERRESTRIAL AIR-BREATHING MOLLUSKS. 



superior tooth on the peristome is lar<:^er and more deeply seated than the in- 

 ferior one, and that the hitter, though more developed, is much of the same 

 form as the inferior tooth in fastigans and Troostiana. The parietal tooth par- 

 takes of the general character of that in Lea's type of Dorfeidlliana, but its 

 lower and terminal margins project more j)erpendicularly from the parietal 

 wall. The umbilical perforation is also larger, and the base of the shell is more 

 smooth. The following are the measurements of a large specimen : Greater 

 diameter 9, lesser 8 mill. ; height, 4 mill. I am much inclined to consider this 

 a distinct species, but remark upon it, as I believe it is more commonly found 

 in cabinets under the name of DorfeuiUiana, than the shell described by Lea. 



P. DorfeuiUiana, and also the shell last considered, have a tubercle within 

 the aperture very similar to that m fastigans and Troostiana. 



Jaw not observed. 



Lingual membrane with 20 — 1 — 20 teeth, the tenth having its inner cutting 

 point split. Marginals as usual in the genus. PI. VL Fig. I. 



Genitalia unobserved. 



Polygyra Ariadnse, Pfr. 



Shell with an arcuate rimation, terminating in a minute oblique perforation, 

 depressed, subdiscoidal, rather solid, nearly transparent, bluish-white, with 

 scarcely perceptible wrinkles on the upper surface ; spire flat- 

 tened ; whorls 5, separated by a distinct suture, flattened, the 

 last one suddenly falling towards the aperture, very much con- 

 tracted and pinched behind the peristome, more convex and 

 smoother below ; there is a deeply chiselled, arcuated, umbilical 

 rimation, the umbilical region is also channelled ; aperture small, 

 extremely complicated with teeth, very oblique, lunately cir- 

 cular, ringent ; peristome white, slightly reflected, its termina- 

 P. AriadncB. tious approaching each other and joined by two flexuose, 

 elevated, acute laminae, converging to a point far within the 

 aperture ; the basal margin of the peristome is also furnished with two stout, 

 entering, converging marginal folds ; the right margin of the peristome has a 

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

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



ffelix Ariadnce, Pfeiffer in Zeitsch. f. Mai., 1848, 120 ; Mon. Hel. Viv., III. 



266 ; in Chemnitz, ed. 2, I. 372, PI. LXV. Figs. 19 - 21 (1846). — W. G. BiN- 



NEY, Terr. Moll., IV. 76, PI. LXXVIIl. Figs. 1, 3, 4 ; L. & Fr.-W. Sh., I. 



104, Fig. 180 (1869). —Fischer and Crosse, Moll. Mex. et Guat., 287, PI. 



XII. Fig. 8 (1870). 

 Helix Couchiana^ Lea, Proc. Acad. Nat. Sci. Phila., 1857, 102 ; Journ. — ; Obs., 



XI. 139, PI. XXIV. Fig. 112. 

 Dcedalochila Ariadnce, Tryon, Am. Journ. Conch., III. 66 (1867). 



