POLYGYRA. 269 



last whorl, which prevails in auriculala, 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. 



Lingual membrane as usual in the genus; teeth 17 — 1 — 17, with 8 laterals. 

 (PL 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 ; lg 



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

 its terminations scarcely approaching each other, but joined by 

 two white, elevated laminae, which are placed at acute angles on J ' , 



r ° P. ventrosula. 



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, 1\ mill. 



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



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



Icon., No. 687 (1852). —W. G. Binney, Terr. Moll., IV. 73, PL 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, found 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 ; 



Fig. 167. 



Lingual dentition of P. ventrosula. 



marginals with 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, sinning ; spire slightly elevated ; whorls 5, flattened, 

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



