234 WEST AMERICAN SHELLS 
the shell, if the fleshy parts have been removed 
or are lost. 
Acmea mitra, Esch., the White 
Cap, Figure 257, generally lives 
below the tide mark, and is sel- 
dom found living, though I have 
occasionally found them at very 
low water. The shell is pure 
white, fairly thick, and has a pleasing appear- 
ance. Many dead specimens are washed up by the 
waves, and they always find plenty of admirers. 
Sometimes the surface of the shell is covered 
with stony alge, giving it a mammillary appear- 
ance, but generally it is smooth. 
Acmea inséssa, Hds., the Seaweed 
Limpet, Figure 258, (Nacella in- 
sessa), 1S a common species, and 
may be found living on the flat, cen- 
Fig. 258 tral ribbons of the great seaweeds 
whieh are so conspicuous along the rocky coast. 
The sides of the shell are flattened and nearly 
smooth, and the apex is rounded. The shell is of 
a dark brown color throughout, and looks as if 
it were made of horn. It is seldom quite so large 
as the picture represents. 
Acmea instabilis, Gld., the Unstable Seaweed 
Limpet, (Nacella instabilis), is larger than the 
last species. The shell is more limpet-shaped, 
and it is narrow, compressed at the sides, smooth, 
brown on the outside and white within. Its length 
is three-fourths of an inch. 
Acmea depicta, Gld., Painted Limpet, (Nacella 
depicta), has a very narrow shell, with straight, 
