LITTORINIDA., 243 
within, not nacreous, prolonged into a short canal below; lip 
subrostrated in the middle; columella edentulous. Operculum 
corneous, paucispiral. R. Sowverbianus, Fischer (1xix, 29). New 
Caledonia. 
Limnorrocuus, E. A. Smith. Shell trochoid, umbilicated, 
without an epidermis, spirally ridged ; aperture non-lirate within, 
with the outer lip oblique, the basal margin broadly sinuated, 
and the columella-edge somewhat reflexed and united to the 
labrum above by a callosity. Operculum horny, paucispiral. 2 
sp. Lake Tanganyika, E. Africa. &. Thomsoni, KE. A. Smith 
(ixix, 30). Remarkably like the genus Plesiotrochus described 
above; indeed it would be difficult to separate them, except by 
the locality ; this, with other very curious forms imitating marine 
genera, occurs in fresh water, as above. 
Micropoma, Meek and Worthen. 
Distr.—M. conica, M. and W. (lxix, 26°. 
Shell small, rather thick, conical, imperforate, composed of 
flattened whorls, the last one of which is more or less angular 
around the middle and little produced below; aperture about as 
high as wide; outer lip simple, straight and oblique in outline; 
columella without folds or plications, inner lip thin and slightly 
reflected at the base of the columella. Surface with revolving 
nodular ridges. 
CycLocHEILA, Conrad. 
Distr.—1 sp. Tertiary ; So. America. 
Pyramidal; aperture circular; labrum expanded, columella 
flattened, subangular at the base; periphery angular; a very 
doubtful little shell, probably fresh water. 
Lacuna, Turton. 
Etym.—Lacuna, a fissure. Syn.—Temana, Leach. 
Disir.—16 sp. Northern shores, Norway, Britain, Spain, 
United States. Fossil. Eocene—. JZ. pallidula, Da Costa 
(ixix, 31). 
Shell turbinated, thin; aperture semilunar; columella flattened, 
with an umbilical fissure ; operculum paucispiral. 
Animal. Operculigerous lobe furnished with lateral wings and 
tentacular filaments. Teeth 5-cusped; uncini 1, 2, dentated, 3 
simple. Spawn vermiform, thick, semicircular. Range, low- 
water to 50 fathoms. 
The Lacunz feed upon sea-weed, and Lovén observes that 
when the fucus is of a brown color, the animals become green, 
but if red, they assume a rosy tint. 
EPHERIA, Leach. Shell thin, with revolving colored bands ; 
spire rather elevated; inner lip thin, sharp. JZ. vincta, Turton 
(Ixix, 32). 
