308 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



peristome far within the aperture at once distinguishes it. The size is not 

 however, any criterion, as I have individuals of Ruyeli only 10 millimetres in 

 diameter, while some of my specimens of inflecta are full 13 millimetres. 



The figure shows an enlarged view of the aperture. 



Animal externally resembling that of T. inflecta. 



Jaw as usual ; about 10 ribs. 



Lingual membrane (PL VII. Fig. K) has 21 1 21 teeth; 6 perfect later- 

 als. The inner laterals (eighth to tenth tooth) have a simple inner cutting 

 point; beyond this it is bifid. 



Genitalia (PI. XV. Fig. E) generally resembling those of tridentata, but dis- 

 tinguished by the genital bladder, which is small, globular, on a duct of equal 

 width throughout its course, not swelling as it approaches the vagina. 



Triodopsis tridentata, SAY. 

 Vol. III. PI. XXVII. 



Shell umbilicated, orbicularly depressed, with crowded rib-like striae, light- 

 horn or chestnut colored ; spire very short ; whorls 5^, rather convex, the last 

 scarcely deflected in front; aperture lunar, subtriangular ; peristome white, 

 reflected, its outer contour rounded, thickened within, its terminations con- 

 verging, joined by a light deposition of callus bearing a tongue-like, erect, 

 entering tooth, both the right and basal portions bearing on the inner margin 

 a stout, acute denticle. Greater diameter 16, lesser 14 mill. ; height, 8 mill. 



Helix tridentata, SAY, Nich. Encycl, PI. II. Fig. 1 (1817-1819); BINNEY'S 

 ed., 6, PI. LXX. Fig. 1. EATON, Zool. Text-Book, 193 (1826). FERUS- 

 SAC, Tab. Syst., 38; Hist., PI. LI. Fig. 3. WOOD, Ind. Supplem., 21, 

 PL VII. Fig. 2 (1828); ed. HANLEY, 226, Fig. 11. DESHAYES, Encycl. 

 Meth., II. 213 (1830); in LAM., VIII. 115 ; ed. 3, 309 ; in FER. 1. c., I. 72. - 

 BINNEY, Bost. Journ. Nat. Hist., III. 382, PL XVII (1840), part; in Terr. 

 Moll., II. 183, PL XXVII. DEKAY, N. Y. Moll., 28, PL II. Fig. 7 (1843). 

 ADAMS, Vermont Mollusca, 160 (1842). GOULD, Invertebrata, 173, Fig. 115 

 (1841). PFEIFFER, Mon. Hel. Viv., I. 412; in CHEMNITZ, 2d ed., I. 84, PL 

 X. Figs. 7, 8. POTIEZ et MICHAUD, Gal., I. 114. MRS. GRAY, Fig. Moll. 

 An., PL CCXCI. Fig. 3 (ex Bost. Journ., nodescr.). REEVE, Con. Icon., No. 

 690 (1852). W. G. BINNEY, Terr. Moll., IV. 70; L. & Fr.-W. Sh., I. 129 

 (1869). BLAND, Ann. N. Y. Lye., VII. 423. MORSE, Amer. Nat., I. 150, 

 Figs. 8, 9 (1867). GOULD and BINNEY, Inv. of Mass., ed. 2, 422 (1870). 



Triodopsis lunula, RAFINESQUE, En. and Ace., 3 ; ed. BINNEY and TRYON, 68. 



Triodopsis tridentata, TRYON, Am. Jouvn. Conch., III. 50 (1867). 



LISTER, PL XCII. Fig. 92. 



From Canada through all Eastern North America. A species of the Eastern 

 Province. 



A curious pathological specimen, with a double peristome, is figured on p. 309 

 Animal dark bluish slate-color, deeper on the head, eye-peduncles, and ten 



