HELIX. 



14V 



its surface smoother, and, above all, its lip is not so broadly re- 

 flected ; it is also distinctly subcarinate at the periphery. 



Helix thyroides, Say. — Shell narrowly iimbilicated, depressed 

 globose ; spire convex ; epidermis of a uniform yellowish-brown or russet 

 color ; whirls five, with fine, parallel strias, running obliquely across them ; 

 spire more or less elevated; suture distinctly impressed ; aperture lunate, 

 contracted by the peristome, the plane of the aperture making a consider- 



Fig. 251. 



Helix thyroides. 



able angle with the plane of the base of the shell ; parietal wall with a 

 protnineut, white, tooth-like process placed obliquely to the axis of the 

 shell ; peristome white, thickened, widely reflected, and sometimes grooved 

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

 partially covered by the reflected peristome where it unites with the base 

 of the shell. Greater diam. 22, lesser 19^ ; height 13 mill. 



Helix thyroides, Say, Nich. Encycl. (Amer. ed.), 1817, 1818, 1819 ; Journ. 

 Phila. Acad. I, 123 (1817) ; Americau Conchology (1831), No. 2, pi. 

 xiii ; ed. Binney, 33, pi. xiii ; ed. Chenu, Bibl. 3, 22, pi. iii, f. 3. — 

 Eaton, Zool. Text-Book, 193 (1&26).— Ferussac, Hist. pi. xlix, a, f. 

 4; pi. 1, a, f. 6?— Deshayes, Encycl. Meth. II, 230 (1830) ; in Lam. 

 An. sans Vert. VIII, 114; ed. 3, III, 309; in Fer. I, 209.— Bixney, 

 Bost. Journ. Nat. Hist. I, 488, pi. xviii (1837) ; Terr. Moll. II, 129, 

 pi. xi.— Leidy, T. M. U. S. I, 257, pi. xi, f. 7-9 (1851), anat.— DeKay, 

 N. Y. Moll. 29, pi. ii, f. 8.— Gould, Invertebrata, 171, f. 108 (1841).— 

 Adams, Vermont Mollusca, 159 (1842). — Mrs. Gray, Fig. Moll. An. 

 pi. ccxci, f. 6, from Bost. Journ., no descr. 



Helix thyroides, Pfeiffer, Mon. Hel. Viv. I, 345 ; in Chemnitz, ed. 2, I, 

 331, pi. Iviii, f. 8, 9 (1850).— Reeve, Con. Icon. no. 677.— W. G. 

 BixNEY, Terr. Moll. IV, 53.— Morse, Amer. Nat. I, 98, f. 3 (1867). 



Anchistoma thyroides, H. & A. Adams, Gen. pi. Ixxviii, f. 3, no descr. 



Mesodon thyroides, Tryon, Am. Journ. Conch. Ill, 41, pi. viii, f. 1 (1867). 



From Canada through all eastern North America, and in the 

 postpleiocene of the Mississippi Valley. 



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