56 



LAND AND FRESH-WATER SHELLS OF N. A. [PART L 



Macrocyclis concava. 



Macrocyclis concaTa, Sat. — Shell depressed, very slightly con- 

 vex on the upper surface ; epidermis whitish horn-color, sometimes with 

 a tinge of green ; whirls five, above flattened, below 

 rounded, finely striate obliquely, and sometimes with 

 microscopic revolving lines ; the outer whirl spreading 

 a little towards the aperture; suture rather deeply 

 impressed ; umbilicus wide, deep, exhibiting all the 

 volutions to the apex ; aperture rounded, somewhat 

 flattened above, its edge frequently tinged with red- 

 dish-brown ; peristome sub-reflected at its columellar 

 extremity, simple above, and in some specimens con- 

 siderably depressed near its junction with the outer 

 whirl ; columella with a thin callus, the edge of which 

 connects the upper and lower extremities of the peri- 

 stome. Greater diam. 21, lesser 16 ; height 7 mill. 

 Helix concava, Say, Joum. Acad. II, 159 (1821) ; Binney's ed. 20. — 

 BiNNEY, Bost. Journ. Nat. Hist. Ill, 372 (1840), excl. pi. ; Terr. 

 Moll. II, 163, pi. xxi. — Adams, Vermont Mollusca, 159 (1842), excl. 

 syn. vancouverensis, — DeKay, N. Y. Moll. 33, pi. ii, f. 15 (1843). — 

 Pfeiffer, Mon. Hel. Viv. IV, 159.— W. G. Bisney, Terr. Moll. IV, 

 63.— Leidy, T. M. U. S. I, 258, pi. xii, f. 9-11 (1851), auat.— Mokse, 

 Amer. Nat. I, 412, f. 26, 27 (1867). 

 Helix planorboides, Fekussac, Hist. Nat. des Moll. tab. Ixxxii, f. 4. — 

 Pfeiffer, Mon. Hel. Viv. I, 200 ; Symbolic, II, 37. — Chemmtz, ed. 

 2, II, 164, pi. xcv, f. 17-19; pi. cliv, f. 45 (1851).— Reeve, Con. 

 Icon. 674 (1852). — Deshayes in Fer. I, 87. 

 Helix dissidens, Deshayes in Fer. Hist. I, 97, pi. Ixxxiv, f. 1, 2. 

 Macrocyclis concava, Morse, Journ. Portl. Soc. I, 12, pi. v, fig. (1864). — 

 Tryon, Am. Journ. Conch. II, 245, pi. iii, f. 8 (1866). 



Fig. 95. 



Canada to Georgia ; Michigan to Missouri. Also in 

 the postpleiocene of Mississippi Yalley. 

 See remarks under 31. vancouverensis. 

 Jaw creseentic, ends bluntly rounded ; anterior sur- 



