LIMPETS. 
39 
with great force, and submit to have their shells 
broken before they will yield. In some countries 
they are eaten, and also vast numbers are gath- 
ered as bait by the fishermen. Notice caretully 
the broad foot, the mantle and gills, the short 
head and tentacles, and the horse-shoe shaped 
muscular impression, inside the shell. 
Acmcea jpatina , Esch., Plate Limpet, Fig. 6, 
PI. X, is oval, flattened, with the apex nearly 
central, and more or less distinct, radiating striae. 
Externally it is dark, often overgrown with moss 
&c; internally, near the edge, there is a dark 
rin<r; often broken into blocks, then a broad, blue- 
white enameled space, and within the muscular 
impression is a patch of brown. Length ol shell, 
one to two inches. 
Acmcea pelta , Esch , Shield Limpet, Fig. 4, 
PI. X, is more conical and pointed, with about 
25 blunt ribs, sometimes obsolete. The outside 
is brownish or striped ; the inside white, with a 
narrow, dark thread round the edge, and a brown 
patch in the center. At Duxbury Keef, in Marin 
Co., I found some old specimens, with very thick 
shells, living in deep depressions which they had 
made in the rock. A small, black, conical shell, 
supposed by Carpenter to be an abnormal growth 
of the young of this species, is now known as 
Acmcea Asmi , Midd. 
Acmcea persona , Esch., Mask Limpet, Fig. 5, 
PI. X, can easily be distinguished from the pre- 
ceding species, by the posterior position of the 
apex. The ribs on the front of the shell are 
prominent, but rough and irregular. Its outside 
color is brownish, or mottled; internally it resem- 
