314 A MANUAL OF AMERICAN LAND SHELLS. 



Avhite, tootb-like process placed obliquely to the axis of the shell ; peri- 

 stome white, thickeued, widely reflected, and sometimes grooved on its 

 face, its exterior yellowish; umbilicus exhibiting only one volution, 



Fig. 835. 



^■' ;• 



JIT. thyroides. 



partially covered by the reflected peristome where it unites with the 

 base of the shell. Greater diameter 22, lesser lO^""'^ ; height, IS""". 



Helix Ihi/roiduF, Say, Nich. Encycl. (Ainer. ed,), 1H17, 1818, 1819 ; Joiirn. Phil. Acad, 

 i, 1-23 (1817); American Concliol()f>y (18.31), No. 2, pi. xiii ; ed. Binnky, 33, 

 pi. xiii; ed. Chenu, Bibl., 3, 22, ])\, iii, fig. 3.— Eaton, Zool. Text-Book, li)3 

 (1826). — Ferussac, Hist., pi. xlix, a, fig. 4; pi. 1, «, fig. 6? — Deshayes, 

 Encycl. M<^th., ii, 230 (1^30); in Lam., An. sans Vert., viii, 114; ed. 3, iii, 309; 

 in Fku., i, 209.— Binxey, Bost. Journ. Nat. Hist., i, 488, pi. xviii (1837); 

 Terr. Moll., ii, 129, pi. xi.— Leidy, T. M. U. S., i, 257, pi. xi, figs. 7-9 (1851), 

 anat.— r3E Kay, N. Y. Moll., 29, pi. ii, fig. 8.— Gould, Invertebrata, 171, fig. 

 108 (1841); ed. 2, 425 (1p70).— Adams, Vermont MoUusca, 159 (1842).— Mrs. 

 Gkay, Fig. Moll. An , pi. ccxci, fig. 6, from Bost. Jouru., no descr. 



Helix thyruidcs, PFEirFER, Mon. Hel. Viv., i, 345; in C'liEMXiTZ, cd. 2, i, 331, pi. Iviii, 

 figs. 8, 9 (1850).— Reeve, Con. Icon., No. 077.— W. G. Bixney. Terr. Moll., iv, 

 53; L. & Fr.-W. Sli., i, 147, fig. 251 (1869).— Mouse, Amer. Nat., i, 98, fig. 3 

 (1867). 



Anchlsioma ihi/roides, II. & A. Adams, Gen., pi. Ixxviii, fig. 3, no descr. 



Mesodon ilujroidts, TuYON, Am. Journ. Concb., iii, 41 (1867). 



Helix hxicculenta, Gould, Proc. Bost. Soc. Nat. Hist., iii, 40 (1848); Terr. Moll., iii, 9, 

 pi. xi, rt.— Pfeiffer, Mon. Hel. Viv., iii, 271; iv, 323. — W. G. Binney, Terr. 

 Moll., iv, 54 ; L. & Fr.-W. Sh., i, 148, fig. 254 (1869). 



Helix thi/roides, (3, Pfeiffer, Mon. Hel. Viv., i, 345. — Var. F£ruS8AC, Hist., pi. 1, a, 

 fig. 7. 



Mesodon bucculcnta, Tryon, Am. Jonrn. Concb., iii, 41 (1867). 



Mesodon thyroides, W. G. BiNMEY, Terr. Moll., v, 330. 



Animal: Color a dirty yellowish-white, with a grajish hue in some 

 individuals, eye peduncles darker, eyes black, base of foot dirty white; 

 foot rather narrow, terminated posteriorly' in an acute angle. Length 

 equal to twice the breadth of the shell. (See Bost. Journ. i^. H., I, 

 Plate VII.) 



A Post-pliocene species, now found over all the Eastern Province. 

 The variation in size of the species is great. The smaller form (from 

 near Philadelphia) is often found imperforate and toothless. (See out- 

 side figures above.) 



A reversed specimen was found by me at Graniteville, S. C. 



Jaw long, narrow, slightly arcuate, with 13 stout ribs on both an- 

 terior and posterior surfaces, denticulating either margin. 



The lingual membrane (Terr. UoW., V, Plate YIII, Fiff, S) has 



