CYCLOSTOMID A. 285 
testaceous externally, flat, paucispiral; the whorls obliquely sil- 
lonated or striated, nucleus very excentric. 
LEONIA, Gray. Peristome simple, subreflected. Operculum 
oval, calcareous, unispiral, convex externally, nucleus lateral, 
near the columellar lip. JZ. mamillaris, Lam. (I1xxvi, 85). 
Southern Europe. 
Cyotostoma, Lam. 
EHtym.—Cyclos, circle, and stoma, mouth. 
Distr.—120 sp. About half in Madagascar, a few in the Kast’ 
and West Indies, two or three in Europe. C. sulcatwm, Lam. 
(Ixxvi, 86). C. elegans, Mull. (Ixxvi, 87). 
Shell globular-conic or turriculated, thin, more or less widely 
umbilicated ; aperture subcircular; peristome single or double, 
straight or slightly reflected. Operculum calcareous, paucispiral, 
flattened, nucleus excentric. 
Animal with clavate tentacles; sole of the foot divided by a 
longitudinal groove, the sides moved alternately in walking; the 
end of the long muzzle is also frequently applied, as by the 
looping-snails (Truncatellz), and used to assist in climbing. 
TROPIDOPIIORA, Troschel. Shell depressed turbinate, widely 
umbilicated or imperforate, with revolving caring and strize; lip 
reflected, sometimes covering a part of the umbilicus. A group 
of usually large species inhabiting Madagascar. C. Cuvierianum, 
Petit (Ixxvi, 88). 
LITHIDION, Gray. Shell depressed, widely umbilicated; aper- 
ture subcircular; peristome simple, thin or thickened. Operculum 
paucispiral, with a strong subcentral carina.  C. lithidion, Sowb. 
(Ixxvi, 89). 
REVOILIA, Bourguignat, 1881. (Dedicated to M. Georges Révoil.) 
Shell depressed, discoidal, spirally ridged; umbilicus wide in 
young individuals, but entirely closed in adults by a thin dilation 
of the columellar lip; peristome continuous, dilated-reflexed, the 
lip slightly ascending against the body-whorl above. &. Milne- 
Edwardsi, Bourg. E. Africa. Closely allied to Lithidion. 
oTopoMa, Gray. Shell subglobose, umbilicated; peristome 
simple or a little reflected, with an ear-like process covering part 
of the umbilicus. Operculum convex in the middle. 19 sp. 
Socotra, Madagascar, Zanzibar, Mauritius, India. C. Naticoides, 
Recl. (Ixxvi, 90). 
LIGATELLA, Martens. Shell rounded, turbinate-conical, usually 
banded; peritreme simple. Cape of Good Hope, Mauritius, 
Madagascar. C. ligatwm, Mull. (Ixxvi, 91). 
GEORGIA, Bourguignat, 1882. (Dedicated to Georges Révoil.) 
Umbilical region entirely covered by a callous expansion of the 
inner lip, which is not continuous with the labrum above. Oper- 
culum perforated in the centre, interiorly concave, spiral, covered 
by a mucilaginous membrane, externally convex, four-whorled, 
