232 WEST AMERICAN SHELLS 
sometimes prettily checked with brown and green. 
Within, the shell is variously marked with brown 
and bluish-white, with a dark ring around the 
edge. The common length of the shell is from an 
inch to two inches. 
Acmea pelta, Esch., 
the Shield Limpet, Fig- 
ure 255, 1s more conical 
and pointed than the 
last, and the outside of é 
the shell has about Hig.258 
twenty-five blunt, radiating ribs. Externally it 
is gray or striped, and is sometimes very beauti- 
ful; the inside is mainly white, though there is 
often a dark thread around the edge, and a brown 
spot in the center. A strange form is sometimes 
found in which the early growth of the shell seems 
to have been formed on a different plan from that 
of the ordinary specimen, for it is smooth, brown, 
and has almost perpendicular sides like the lim- 
pets that grow on seaweeds; but after that it sud- 
denly changes to the ordinary form. Itis probable 
that this was caused by a decided change in the 
abode of the limpet, perhaps from the seaweed to 
the rock. 
A small, black, conical shell, supposed by Car- 
penter to be an abnormal growth of the young of 
this species is now known as Acmea asmi, Midd., 
the Black Limpet. It is usually found living on 
the shells of the Black Turban, and is only one- 
fourth of an inch in length, while the ordinary 
shells of the last species are an inch long or more. 
