MACROCYCLIS. 405 



Ilelix Unmta, Say, Journ. Phila Acad. i. 18 (1817) ; ii. 273 (1824) ; Nich. Encyc. 3d cd. 

 iv. (1819) ; Binney's cd. 7, 24. — Binney, Bost. Journ. Nat. Ilist. iii. 436, pi. 22, 

 fig, 6 (1840) ; Terr. Moll. ii. 2G1, pi. 48, fig. 1. — De Kay, N. Y. Moll. 44 (1843). 

 — Gould, Inv. 179, fig. 103 (1841). —Adams, Vermont Moll. 161 (1842).— 

 Ferl-s.sac, Tab. Syst. 44 ; Hist. pi. 79, fig. 1. — Desha yes in Fer. i. 80. — Chem- 

 nitz. 2d cd. ii. 203, t. 101, figs. 13 - 1.5. — Pfeiffer, Mon. Hel. Viv. i. 184. — 

 Keeve, Con. Icon. 724 (1852) — W. G. Binney, Terr. Moll. iv. 123. —Morse, 

 Amcr. Nat. i. 546, fig. 44 (1867). 



Pltiiwrbis paraUeliis, Say? Jouni. Phila. Acad. ii. 164 (1821) ; ed. Binney, 63. 



Ilelicodisciis linentn, Morse, Journ. Portl. Soc. i. 25, figs. 61, 62; pi. 2, fig. 3; pi. 8, fig. 

 63 (1664). — Tryon, Am. Journ. Conch, ii. 264, pi. 4, fig. 60 (1866). 



Shell minute, discoidal, flat above, concave beneath, greenish ; 

 whorls abont four, flat above, higher than broad, sep- 

 arated by a distinctly impressed suture, covered with Fig. 667. 

 numerous, parallel, raised, revolving lines ; otherwise 

 smooth ; aperture narrow, semi-lunar ; lip simple and 

 thin : umbilicus wide and deep, exhibiting each volu- 

 tion to the apex. Within the aperture, on the exter- 

 nal wall, are placed two pairs of white conical teeth, 

 the first pair in sight on looking into the aperture, 

 the other more remote, and seen only through the 

 semi-transparent shell. Diameter, one eighth of an Enlarged" 

 inch, usually less. 



Animal whitish, transparent, thread-like. 



It has been noticed, for the most part, under the bark, or in the 

 interstices, of rotten wood ; sometimes under stones and leaves in 

 damp places. Inhaliits all of Eastern North America, having been 

 found i'roni Gaspe to Texas ; also on the Rio Chama, New Mexico. 



At first sight one would be disposed to call this shell a Planorbis 

 rather than a Helix. Perhaps it is the P. parallelus of Say. Its 

 wheel-shaped form, greenish color, revolving raised lines, and sin- 

 gular teeth, are characters which cannot be mistaken. One pair of 

 these teeth may always be found and seen ; and in one instance Dr. 

 Binney noticed even a third pair still farther within the whoii. 



Genus ITI.ICROCVCLIS, Beck. 1837. 



Shell thin, widely umbilicated, depressed, striate or wrinkled, 

 color uniform ; whorls four and a half to five, the last broad, de- 

 pressed, moderately deflcxed in front, aperture obliquely ovate ; 

 peristome somewhat thickened or expanded, the margins approx- 

 imating, the basal shortly reflexed. 



