THES ROCK SHELLS: 
FRANK COLLINS BAKER, 
Curator of the Chicago Academy of Sciences. 
HE rock shells or murices are 
among the most beautiful and 
interesting of all the mollusks 
or Shell fish, and are a favorite 
among collectors. Their peculiar 
spiny shells and brilliant colors caused 
them to be among the first mollusks 
studied by naturalists and we find 
them, therefore, described in the 
earliest works on natural history. 
There are about two hundred dif- 
ferent kinds of rock shells, mostly con- 
fined to the tropical and subtropical 
seas, although a few are found in tem- 
perate climes. The greatest number 
of these are found about rocks at low 
water but not a few are inhabitants of 
waters as deep as fifty fathoms or 
more. In our own country they are 
abundant along the coast of Panama, 
the Gulf of California, Florida and the 
islands of the West Indies, but the 
largest number of varieties comes from 
the Indian Ocean, Japan, the Philip- 
pines and Australia. The more 
brightly colored varieties are from 
tropical seas, while the dull, plain 
species are from subtropical or tem- 
perate climes. 
The murices are peculiar in having 
their shells ornamented by numerous 
projections, which vary from long, 
needle-like spines to simple fluted 
frills. What these spines and frills are 
for would probably puzzle the ordinary 
observer, as they would seem at first 
sight to be inthe way. In some cases 
they are simply ornamental, but in the 
main they are protective and enable 
the animal to escape being eaten by 
some voracious fish. This is known as 
protective adaptation and was probably 
brought about in this manner: the 
murices, or their ancestors, did not at 
first have spiny shells, and they fell an 
easy prey to the fishes. As time went 
on a few individuals, through some 
modification of environment, developed 
small spines or prominences. The 
animals having these were not eaten 
191 
by fishes as the knobs and spines 
caused the fishes pain when swallowed, 
therefore they preferred the animals 
with smoother shells. In time this 
modification caused a weeding-out pro- 
cess, the animals with smoother shells 
being exterminated and those with 
spiny shells increasing in numbers and 
becoming more spiny as one generation 
succeeded another. This continued 
until the present time and is going on 
even now. 
Another interesting fact concerning 
the development of this ornamentation 
is that the smoother shells inhabit 
rocky shores where the waves are con- 
stantly beating in with greater or lesser 
violence, while the more spiny in- 
dividuals live in protected and com- 
paratively still water. This adds ad- 
ditional weight to the theory expressed 
in the last paragraph, for the fish which 
feed upon these shells do not, as a 
rule, inhabit localities where the water 
is rough, as along a rocky shore, but 
live abundantly in protected bays and 
lagoons in which the spiny murices are 
found. 
There are shown on the plate eight 
species of rock shells, all more or less 
common. The first one for us to con- 
sider may be called Venus’ Comb, 
(Murex tribulus) and is found in China, 
Japan and the Indian Ocean. It be- 
longs to a group of shells which is 
characterized by a long snout or canal, 
and long, pointed spines. The color is 
yellowish; in one variety the spines 
are tipped with black. 
A shell which is found onthe mantel 
in every household is known as the 
Branched Rock Shell (Murex ramosus), 
which is widely distributed, being 
found in the Red Sea, the Indian 
Ocean, New Zealand, Australia and the 
Central Pacific Ocean, and attains a 
large size, some specimens reaching 
the length of a foot and weighing 
several pounds. The aperture is fre- 
quently tinged with a deep, beautiful 
