326 TERRESTRIAL AIR-BREATHING MOLLUSKS. 



Mountains in Cherokee County, North Carolina : a species of the Cumber- 

 land Subregion ; also in Rutherford County, North Carolina. 

 Jaw as usual in the genus : 10 ribs. 

 Lingual membrane (PI. XVI. Fig. E) with 40140 teeth. 



Mesodon exoleta, BINNEY. 

 Vol. III. PL X. 



Shell imperforate, convex, somewhat ventricose ; epidermis of a uniform yel- 

 lowish-horn, or russet-color ; whorls between 5 and 6, with fine, parallel strife 

 crossing them obliquely ; body- whorl large and ventricose ; suture well marked 

 and distinct ; aperture rounded, contracted by the peristome, the plane of the 

 aperture making a considerable angle with the plane of the base ; peristome 

 thickened, white, reflected, its basal portion subdentate ; parietal wall with a 

 prominent, white, oblique tooth ; umbilicus covered. Greater diameter 28, 

 lesser 23 mill. ; height, 1 7 mill. 



Helix exoleta, BINNEY, Terr. Moll., II. 131, PI. X. LEIDY, T. M. TJ. S., 256, 

 PL X. Figs. 1-3, anat. DEKAY, N. Y. Moll., 27, PL II. Fig. 6. W. G. 

 BINNEY, Terr. Moll., IY. 54 ; L. & Fr.-W. Sh., I. 144 (1869). 



Helix zaleta, BINNEY, Bost. Journ. Nat. Hist., I. 492, PL XX. MRS. GRAY, 

 Fig. Moll. An., PL CXCI, Fig. 9, from Bost. Journ., no descr. PFEIFFER, 

 Mon. Hel. Yiv., I. 316. DESHAYES in FER.,!. 139. REEVE, Con. Jcon., 

 No. 622 (1852). 



Helix albolabris, var., FERUSSAC, PL XLVI. a, Fig. 6. PFEIFFER, Symb., II. 

 22 (no descr.) ; in CHEMNITZ, ed. 2, I. 81, PL X. Figs. 19, 20. 



Mesodon exoleta, TRYON, Am. Journ. Conch., III. 39 (1867). 



A Post-pleiocene species, now found in the Interior Region. From Western 

 New York and Pennsylvania to Missouri ; from Georgia and Alabama to 

 Illinois. 



Animal grayish-brown or blackish above, paler on the posterior extremity 

 and base; eye-peduncles black, long, and slender; glands very prominent; 

 length, when fully extended, including the eye-peduncles, equal to thrice the 

 breadth of the shell. (See Bost. Journ. Nat. Hist., I. PL IX.) 



Though resembling M. albolabris in many respects, it differs in general 

 aspects, and in many very observable particulars. It is smaller, more convex, 

 and the body-whorl is more ventricose than in that species. The peristome is 

 less flat and broad, and is sometimes a little grooved. The aperture is more 

 round, and the plane of the mouth, instead of being flattened in the direction 

 of the plane of the base, is much more upright, making a considerable angle 

 with the base of the shell. Attention to these differences will enable one to 

 distinguish the shell, even before the tooth is added. In those individuals 

 where the tooth is wanting, there is often a slight deposition of testaceous 

 matter in its place, not distinguishable without close observation. In its geni- 

 talia it has decided specific distinction (see p. 319). 



