200 A MANUAL OF AMERICAN LAND SHELLS. 



mella with n thin calhis, the edge of which connects the upper and lower 

 extremities of the peristome. Greater diameter 21, lesser 16 """ ; height. 



Helix concava, Say, Jouru. Acad., ii, 159 (1821); Binney's ed., 20.— Binney, Boat. 



Journ. Nat. Hist., iii, 372 (1840), excl. pi.; Terr. Moll., il, 163, pi. xxi.— 



Adams, Vermont MoUusca, 159 (1842)^ excl. syn. Vancouver ensis. — De Kay, N. 



Y. Moll., 33, pi. ii, fig. 15 (1843).— Pfeiffer, Mon. Hel. Viv., iv, 159.— W. G. 



BiNNEY, Terr. Moll., Iv, 63.— Leidy, T. M. U. S., i, 258, pi. xii, figs. 9-11 



(1851), auat.— Morse, Amer. Nat., i, 412, figs. 26, 27 (1867). 

 Helix planorhoides, Ferussac, Hist. Nat. dcs Moll., tab. Ixxxii, fig. 4. — Pfeiffer, 



Mon. Hel. Viv., i, 200; Symbola^, ii, 37.— Chemnitz, ed. 2, ii, 164, pL xcv, figs. 



17-19; pi. cliv, fig. 45 (1851).— Eeeve, Con., Icon., 674 (1852).— Deshayes, in 



F^R., i, 87. 

 Helix dissidens, Deshayes, in F]er., Hist , i, 97, pi. Ixxxiv, figs., 1, 2. 

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



Jonru. Conch., ii, 245 (1866).— W. G. Binney, L. & Fr.-W. Sh., i, 56 (1869); 



Terr. Moll., v, 92.— Gould and Binney, Inv. of Mass., ed. 2, 406 (1870). 



A Post-pleiocene species still existing in full vigor in the Eastern 

 Province. Eanges from Canada to Georgia, from Michigan to Mis- 

 souri. The finest specimens occur in the southern part of the Appa- 

 lachian chain. 



Aniinal: Upper surface grayish, tentacles and eye-peduncles bluish, 

 base dirty-white, collar reddish-orange, posterior extremity slightly 

 tinged with the same; eye-peduncles slender, foot narrow, twice as 

 long as the diameter of the shell. 



This shell, though frequently seen, does not seem to be so numerous 

 in our forests as some other species. It is peculiar for the elegant, 

 rounded shape of the whorls as seen on their lower surface. It rarely 

 varies from the common type, and cannot be mistaken for any other 

 Eastern species. The animal is voracious in its appetite, almost always 

 preying upon other species with which it may be kept, and so certainly 

 destroying them that I have been obliged to keep them by themselves. 

 Th's it effects by inserting its narrow body, which it has the power of 

 elongating and protruding very far from its own shell, into the shells 

 of its victims, and then feeding upon them at its leisure. It burrows 

 in the soil under decaying logs. 



See remarks under M. Vancouver ensis, (p. 82). 



Jaw crescentic, ends bluntly rounded ; anterior surface striated ; con- 

 cave margin smooth, with a median projection. (See Terr. Moll., I, Plate 

 Xir, Fig. XI.) 



Lingual dentition (Terr. Moll., V, Plate I, Fig. C) : see above, p. 80. 



Genitalia figured by Leidy in Terr. Moll., I, Plate XII, Figs., 9-11. 

 The general arrangement is the same as in M. Vancouverensis, but the 

 epididymis is less developed. 



