Root Murex Burnt Murex Purple Murex Venus Comb Apple Murex Branched Murex Horned Murex Two-colored Murex] THE ROCK SHELLS. FRANK COLLINS BAKER, Curator of the Chicago Academy of Sciences. The 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 different kinds of rock shells, mostly confined to the tropical and subtropical seas, although a few are found in temperate 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 Philippines and Australia. The more brightly colored varieties are from tropical seas, while the dull, plain species are from subtropical or temperate 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 in the 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 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 process, 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.