GASTEROPODA. 361 
tral. The surface is marked with slightly elevated, rounded, radia- 
ting ribs, of which some twelve are more developed than the inter- 
vening ones, and of a paler colour. The lines of increment are 
crowded, and rather loosely adhering, giving the surface a slightly 
scaly appearance; the general colour is pale ashy-green, with tints of 
violet, especially between the ribs and on old specimens. ‘The interior 
is pale livid, with whitish radiations corresponding to the ribs; the 
margin is paler, sharp, somewhat lobed (in young specimens) by the 
projection of the larger ribs. Muscular impression faint. 
Length nine-twentieths of an inch; width seven-twentieths ; height 
three-twentieths of an inch. 
Inhabits Rio Janeiro. 
Allied to S. plicata, Quoy : which, however, is described as solid ; its 
summit inclined backwards; its ribs equal; its interior pale horn- 
colour, radiated with pairs of reddish lines; and it is also an inhabi- 
tant of a very distant locality,—the Tonga Islands. 
Figure 466, the exterior of the shell; 466 a, profile of the shell and 
animal; 466d, the animal, from below ; 466 c, interior of the shell. 
SrpHonarta Lessont (BLAINVILLE), Malacol., pl. 44, f. 2. D’Or- 
picny; Amer. Merid., p. 56, f. 12-14, Lamarck ; Anim. sans Vert., 
vil. 562. 
Animat deep purplish or bluish black, finely speckled with white 
dots, and with a faint, ochreous margin to the foot. Cephalic mass 
very broad and deep, slightly notched in front; eyes apparent, ap- 
proximate, at its median anterior portion; underneath pale ochreous, 
as is the foot, with a slaty hue in addition. In some individuals the 
foot is altogether a pale slate-colour. Siphonal duplication adherent 
at its anterior portion to the margin of the mantle, and extending 
nearly parallel with it as far as the respiratory cavity, whence it is 
prolonged outwardly in the form of an oblong flap, whose margins are 
undulate or plicate, and its posterior end free. Mantle pale slate- 
colour, its margins ornamented with short, black lineations, corre- 
sponding to the crenulations on the margin of the shell. In young 
91 
