PERIWINKLES. 
29 
ture is purple. Both of these species are very 
interesting for study. They can easily be ex- 
amined in little tide pools, while in motion, and 
their method of clinging to the rock when the 
water has left them should be noted. A near 
relative to the above is the little Lacuna unifas- 
ciata , Cpr., or Chink-shell, represented in Fig. 
I, PI. VII. It is a very little thing, about one- 
sixth of an inch long, very few whorled, brown 
and glossy, with the color sometimes broken into 
dots on the keel of the body whorl. The aper- 
ture is semi-lunar, and the columella flattened, 
with an umbilical fissure, from which it takes 
its generic name. It is worth looking for. 
I^acuna solidula , Lov., is sometimes halt an 
inch in length, but often of less size. It is 
three whorled, strong, smooth, with small um- 
bilicus, brown surface and white columella. 
We have now come to the Trochidce or Top- 
shells, one of the most prominent and numerous 
families on the coast. They vary greatly in 
many respects, but still have the family traits, 
and family feat ures. Some of them are the first 
to greet you as you climb down the rocks to the 
shore, others are rare and shy enough ; some 
have little beauty, while others rival the rainbow 
in their tints. They are mostly conical, with 
entire apertures, and nacreous, or pearly, interi- 
ors. When the outer coats are removed with 
acids, the inner pearly layers appear. The ani- 
mals feed on marine vegetation. We will begin 
our description with the smallest species, Phctsi- 
anella compta , Grid., Pheasant-shell, shown some- 
what magnified in Fig. 3, PI. VII. It is so small 
