rOLYGYRA. 



2G9 



Fig. 166. 



last ■whorl, which prevails in auriculata, and the forms represented by Dr. Bin- 

 ney as varieties of it. It is very rare in collections : I know of but two speci- 

 mens of it. 



Jaw with over 12 ribs. 



JJn<;ual nienibranc as usual in the genus; teeth 17 — 1 — 17, with 8 laterals, 

 (in. XV. Fig. L.) 



Polygyra ventrosula, Pfeiffer. 



Shell rimately perforated, globosely depressed, thin and shining, pellucid, 

 delicately striated, horn-colored ; spire slightly raised ; whorls 5, but little con- 

 vex, the last one subangulated above, falling suddenly towards 

 the aperture, inflated below, anteriorly gibbous and contracted ; 

 aperture very oblique, ringent ; peristome acute, broadly reflected, 

 its terminations scarcely approaching each other, but joined by 

 two white, elevated laminas, which are placed at acute angles on 

 the parietal wall ; the basal margin is also furnished with two 

 white acute denticles ; on the right margin is placed a white sub-perpendicular, 

 extended lamina. Greater diameter 13, lesser 11 mill. ; height, 7^ mill. 



Helix ventrosula, Pfeiffer, Proc. Zool. Soc. 1845, 131 ; Mon. Hel. Viv., I. 417 ; 



in Chemnitz, ed. 2, I. 373 (1846), PI. LXV. Figs. 5, 6 (1849). —Reeve, Con. 



Icon., No. 687 (1852). —W. G. Binney, Terr. Moll., IV. 73, PI. LXXVII. 



Fig. 14; L. & Fr.-W. Sh., I. 92, Fig. 164 (1869). —Crosse and Fischer, 



Moll. Mex. et Guat. 274 (1870). 

 Dcedalochila ventrosula, Tryon, Am. Journ. Conch., III. 63 (1867). 



A Mexican species, ft)und also in the Texas Subregion. 



Jaw strongly arcuate, of uniform width, ends blunt, anterior surface with 8 

 broad ribs, crenulating both margins (see Fig. 157, p. 263). 



Lingual membrane with 93 rows of 24 — 1 — 24 teeth each, 9 laterals ; cen- 

 trals tricuspid, the side cusps very small ; laterals of same shape, but bicuspid ; 



p. ventrosula. 



Fig. 167. 



L»««««*<^" 



Lingual dentition of P. ventrosula. 



marginals w^ith one inner, oblique, bluntly bifid cutting point, and one smaller 

 outer cutting point. 



Polygyra Hindsi, Pfeiffer. 



Shell narrowly umbilicated, depressed, delicately striate, brownish horn- 

 color, diaphanous, thin, shining ; spire slightly elevated ; whorls 5, flattened, 

 the last deflected at the aperture, more convex and constricted below ; umbili- 



