376 



TERRESTKIAL AIR-BREATHING MOLLUSKS. 



Fig. 260. 



E. Tryoni. 



horn-color ; whorls 5 to 6, scarcely convex, the last globose, descending towards 

 the aperture, inflated below ; aperture oblique, subcircular, small, within dark 

 above, lighter below ; peristome thickened, dirty white, its 

 terminations somewhat converging, joined by a light cal- 

 lus, right margin slightly expanded, not reflected, that of 

 the columella dilated, scarcely reflected, appressed, ob- 

 tusely subdentate. Greater diameter 24, lesser 20 mill. ; 

 height, 14 mill. 



Helix Tryoni, NEWCOMB, Proc. Cal. Acad. Nat. Sci., III. 

 116 (1864). W. G. BINNEY, Am. Journ. Conch., I. 47, 

 PI. VI. Figs. 1-10 (1865) ; L. & Fr.-W. Sh., I. 178 (1869). 

 Polymita Tryoni, TRYON, Am. Journ. Conch., II. 319 (1866). 



California Region, on Santa Barbara Island and San Nicholas Island, Califor- 

 nia, both recent and fossil, the latter form very large and thick ; not on San 

 Clemente. 



The species varies in the greater or lesser development of the spire, and in 

 coloring. The form figured differs from that described in having the under as 

 well as upper surface mottled, not a dead white ; an albino form is also found ; 

 also a fourth variety of a uniform cream-color, showing, however, slight traces 

 of the revolving band. 



The animal is black. It has a thick, white, parchment-like epiphragm. 



Jaw arcuate, of uniform width throughout, ends blunt ; anterior surface with 

 stout ribs, denticulating either margin. Figures of the jaws of nine mature in- 

 dividuals are given, showing that the number and arrangement of the ribs is 

 not constant ; a fact noticed in other species. 



Fig. 261. 



Jaws of E. Tryoni. 



