A terrestrial shell, varying considerably in form, but distinguished by
a round aperture, reflected lip, and horny operculum.
Shell more or less elevated, volutions rounded, summit papillose;
aperture round, the edges united circularly and reflected; the left
having its origin very detached from the spire.
Operculum calcareous, complete, not spiral; summit sub-central.
Cyclostoma planorbula.
C. volvulus.
C. carinata.
C. sulcata.
C. unicarinata.
C. tricarinata.
C. obsoleta.
C. rugosa.
C. labeo.
C. interrupta.
C. ambigua.
C. semilabris.
C. flavula.
C. patulum.
C. fasciata.
C. mumia.
C. quaternata.
C. ferruginea.
C. decussata.
C. lineolata.
C. mamillaris.
C. ligata.
C. lincinella.
C. orbella.
C. fimbriata.
C. multilabris.
C. elegans.
C. truncatulum.
_C. elegans._ The elegant Cyclostoma. Pl. 19, fig. 5.
Species with spire slightly elevated, ovate, conical, umbilicated;
volutions convex; finely striated transversely.
_C. fasciata._ The banded Cyclostoma.
Species with spire very elevated.
_C. Planorbula._ The Planorbis-shaped Cyclostoma.
Species with spire very depressed.
FAMILY VIII.
LYMNÆCEA. Three genera.