358 LITTORINID. 
white. Operculigerous lobe small ; the alze anteriorly are mere 
lines, but exposed posteally in flat limited curves, carrying 
far behind a suborbicular, pale yellowish-white, very indistinct, 
paucispiral operculum, obliquely finely interstriated, with a 
sunken nucleus : no caudal cirrhus: the edge of the operculum 
is marked with a fine brown line. 
The animal is free, but the progression is not direct; it 
often jerks or screws the shell a quarter of a round, and carries 
it almost perpendicularly ; it is abundant in the middle littoral 
levels near Exmouth. 
Though this species differs in many points from the typical 
Rissoe, still there is nothing so essentially different as to 
require a new genus; and I am of opimion that the newly 
constituted genera Paludinella and Hydrobia are unnecessary, 
and not generically separated from Rissoa. 
R. tvconspicua, Alder. 
R. inconspicua, Brit. Moll. iii. p. 113, pl. 76. f.7, 8, and pl. 82. f. 5-9. 
R. pulcherrima, Brit. Moll. i. p. 129, pl. 85. f. 1, 2. 
Turbo albulus ? Adams, Linn. Trans. ii. pl. 13. f.17, 18. 
Shell ovately conic, pointed, with 6-7 moderately-raised 
volutions, very pale yellowish-white, marked with two rows of 
longitudinal, distantly separated, dull yellow or rufous irre- 
gular linear blotches on the body, and one on the antepenulti- 
mate whorl. The sculpture is very variable, sometimes almost 
smooth, at others with close-set, longitudinal costellz, showing 
all the phases of strong and fine lines, crossed at right angles 
by finer ones. There are one or two grooved circular lines at 
the base of the body volution. The aperture is suborbicular, 
and the outer lip has the callous pad of the Rissoe. Axis 
ith, diameter ;1,th of an inch. 
Animal. Ground colour white, blotched with yellow and 
dark smoke hues. Mantle entire, except that at the upper 
angle of the aperture it has the pendant filament so often 
seen in the Rissow, and the use of which still remains doubt- 
ful. Rostrum short, cloven, carrying the buccal disk beneath, 
with its vertical fissure, and the usual masticatory apparatus 
of a pair of jaws, corneous palate, and tongue; it is tinged 
