288 CYCLOSTOMIDA. 
lirated. Operculum truncate, conoid, concentric, multispiral ; 
internally membranous, externally shelly ; external margins of 
the whorls raised in the form of shelly plates, incurved ; some- 
times sculptured. 
Animal white, with a short oval foot, undivided beneath ; 
tentacles small, black, with eyes at the base. 
Cyciotus, Guilding. 
Syn.— Poteria, Gray. 
Distr.—120 sp. Tropical, world-wide. C. planorbulus, Lam. 
(xxvii, 10). 
Shell subdiscoidal, very widely umbilicated ; aperture circular, 
entire; peristome straight or sometimes reflected. Operculum 
orbicular, calcareous, a little concave exteriorly. 
APEROSTOMA, Troschel. Peristome forming a posteriorly pro- 
jecting angle, not reflected. Operculum with ridged whorls. 
C. asperulus, Sowb. 
cyRTOoTOMA, Morch (Adams). Last whorl free, cylindrical ; 
aperture rounded, the left margin dilated, angulated and pro- 
duced posteriorly. (C. Mexicanus, Menke (Ixxvii, 12). 
AMPHICYCLOTUS, Crosse and Fischer. Operculum horny, mul- 
tispiral, with a central, wart-like projection inside. Type, C. 
Boucardi, Salle. Mexico. 
OpisTHOPHORUS, Benson. 
Mistr.—16 sp. Siam, Java, Borneo, Sumatra. O. biciliatus, 
Mouss. (Ixxvii, 13). 
Shell depressed, widely umbilicated; suture with a small open 
tube; peristome double. Operculum calcareous, rather thick, 
double, with concamerations between the two disks, which are 
both concave, the interior one with a corneous epidermis. 
MICHOPOMA, Blanford. Shell turbinate; epidermis fuscous, 
thick, hirsute; aperture corrugate within. Operculum multi- 
spiral, calcareous without, corneous within. 2sp. India. 0. 
hirsutus, Beddome (Ixxvii, 14). 
Rau1ostomMA, Benson. 
Htym.—Rkhion, a promontory. 
Distr.—6 sp. Siam, Cochin China. O. Haughtoni, Benson 
(Ixxvii, 15). 
Shell subdiscoidal, broadly umbilicated ; last whorl separate, 
laterally descending; aperture free, with an incision at the top, 
and a subtubular prominence crowning the slit. Operculum 
multispiral. 
cycLosurus, Morelet, 1881. Shell with three embryonal spiral 
whorls, then disjoined and becoming tubular ; aperture circular, 
peristome continuous, simple. Operculum corneous, multispiral. 
