20 SHELL GALLERY. 
Cases The family of Muricidw, or " Rock-shells," is another extensive 
group, containing many very handsome and peculiar forms. The 
animals of this family have a long proboscis, at the end of which 
is the spiny tongue (radula), and which is retractile within the 
body. The true Murices produce at intervals ribs or varices, which 
in some species are ornamented with long spines or foliations, and 
which indicate periods of growth, but of what duration we do not 
know. They are all carnivorous, feeding chiefly on other Mol- 
lusca, boring through the shells of bivalves with their spiny tongue, 
and slowly devouring the unfortunate inhabitant piecemeal. From 
certain species of Murex (M. Irandaris, &c.) found in the Mediter- 
ranean, the ancients manufactured the celebrated Tyrian purple dye. 
Cases The " Purples " {Purpura) are found between tide-marks all 
74-75. over the world. Magilus, belonging to the family Coralliophilida 
(Case 77), is found among coral-reefs in tropical seas, and has the 
remarkable habit of lengthening the aperture of its shell into an 
elongate tube, in order to keep pace with the growth of the coral, 
and to prevent its being overgrown and killed. 
Cases The "Volutes" (Volutidai) are a group of shells also much 
78-81. sought after by shell-collectors. Some of these attain to a very large 
size, the animals inhabiting them being enormous. The Boat- 
shells (Cyrnba) and Melons (Cymbium) are ovo-viviparous, the young 
being carried about by the parent until they are an inch in length. 
Volutes are found chiefly in the warmer parts of the Atlantic and 
Indo-Pacific Oceans, and occur in the greatest variety on the coasts 
of Australia. 
Cases The Olives (OUvidai) are common in most tropical seas, and are 
81-83. remarkable for their beautiful polish and various patterns of colour- 
ing. In structure and form they are very similar to each other. 
They burrow in sand in quest of bivalves for food, and some species 
are said to have the power of swimming by expanding the lobes of 
the foot. 
Case 84. The Harps (Harpidce) form a small well-marked group, of which 
probably nearly all the existing species have been discovered. The 
animals inhabiting these beautiful shells are also brightly coloured. 
They have the remarkable power of casting off a portion of the foot 
when disturbed. The species are known from the Indo-Pacific Ocean, 
the west coast of Central America, and West Africa. 
Cageg The next family, the "Slit-lips" (Plevrofomatidce), consists of 
85-87. very numerous species, over a thousand living forms having been 
discovered, and almost as many fossil species from Cretaceous and 
