362 LITTORINID A. 
the external bases. ‘The foot is nearly the shape of the type, 
contracted in the middle, pomted behind, and sometimes 
emarginate, but it is proportionately longer, larger, and 
thicker; there is no groove or longitudinal line on the sole ; 
the upper lobe anteally expands into narrow white wings, and 
terminates behind with three caudal processes, whereof the 
middle is the longest, and writing of it to Professor Forbes, I 
termed it a “bashaw with three tails”; it carries the lght 
corneous suboval operculum at some distance from the end of 
the foot, but the first two turns of the spire are nearly obso- 
lete ; the third occupies the greater portion of the plate, and 
is well marked with oblique lines of growth. 
I have lately examined many lively specimens, and can 
confirm the fact of the operculigerous lobe terminating in 
three filaments, as well as the presence of the short mantellar 
process, that is produced and retracted at the will of the animal, 
from the upper angle of the aperture. What are the func- 
tions of this organ is doubtful; it has not the aspect, nor the 
position, of a reproductive element; it has more the resem- 
blance of a tentacular instrument; but in some Rissoe it 
acquires an imperfect tubular appearance, as in the Chem- 
nitzie, in which, particularly Ch. acuta, it seems to perform 
the office of the branchial siphon of the Canalifera. I believe 
that this appendage has scarcely been noticed by authors ; it 
appears to exist in many of the Rissoe, but if in all is doubt- 
ful; it has no connection with the operculigerous lobe, or its 
wings or caudal cirrhi, but is a strictly mantellar process. 
The animal is free, unusually rapid on the march, inhabits all 
the zones, and has not been before observed. 
R. costata, Adams. 
R. costata, Brit. Moll. iii. p. 92, pl. 78. f.6, 7, and iv. p. 263, 
Animal inhabiting an elaborately sculptured, costated, spi- 
rally striated, basally ridged, pale yellow shell, of 5-6 rounded 
volutions, hyaline-white, except the large black eyes and pale 
red buecal disk. Head a long proboscidiform muzzle, finely 
corrugated in quietude, cloven vertically at the orifice, as im 
R. parva, but showing more partially than m that species the 
