318 THE MA GIL US. 



fissure is caught against the sharp front edge of the shell, and thus undergoes involuntary 

 amputation. 



The general colors are tolerably similar throughout the Harps, but each species always 

 preserves its peculiar individuality. One species, for example, has the spaces between the 

 ridges pencilled in elaborate wavy markings of chocolate on white, and the ribs themselves 

 barred at regular intervals bylines of deep brown; while another, known by the name of 

 Ventricose Harp (Harpa ventricbsci), has the spaces tilled with a succession of arches, one 

 within the other, and of a rich brown color. 



A very common slnll may often be found on the seashore, looking like a small whelk with 

 a smooth whitish shell, boldly banded with reddish-brown. This is the Common Purple, or 

 Purpura ( Purpura lapillus), another member of this genus, and worthy of notice as being one 

 of the shells which furnish (he celebrated Tyrian purple of the ancients. This color, which, 

 by the way, contains so little blue as to lie unlike the tint which we now call by the name of 

 purple, is evidently the analogue of the ink found in the sepia, and is secreted in a little sac 

 by the throat, containing only one small drop. 



For the very best dye this material was extracted carefully from the individual shells, but 

 for an inferior kind it was obtained by pounding a quantity of the Purpura? in a mortar, and 

 straining off the juice, which was thus mixed with the blood and general moisture of the 

 animals, and consequently of less value than the pure dye. So expensive was the dye obtained 

 by this latter process, that a pound of wool stained with it could not be purchased under 

 a sum equalling one hundred and fifty dollars. Anyone can try the experiment of dyeing 

 a little strip of linen with the matter obtained from a single shell. After breaking the shell 

 carefully so as not to crush the inhabitant, the cell containing the coloring matter will be seen 

 lying across the head or neck of the animal, and can be removed by opening the sac and 

 taking up the yellowish-white contents with a small camel' s-hair brush, or the point of a new 

 quill-pen. When the linen is imbued with this liquid and placed in the rays of the sun, it 

 immediately begins to change its color, and passes through a series of tints with such rapidity 

 that the eye can hardly follow them, unless the slanting rays of the rising or setting sun are 

 chosen for the purpose. 



One of the strangest, though not the most beautiful, of shells is the Magilus, a native of 

 the Red Sea and the Mauritius. 



During its stages of development, the Magilus appears once as a small and delicate shell 

 and then as a long, crumpled, and partly spiral tube, with a shell at one end and an opening 

 at the other. 



For tlie purpose, apparently, of carrying out some mysterious object, the Magilus resides 

 wholly in the masses of madrepore, and in its early youth is a thin and delicate shell without 

 anything remarkable about it. As it advances in age, it enlarges in size, as is the case with 

 most creatures ; but its growth is confined to one direction, and, instead of enlarging in diam- 

 eter, it merely increases in length. The cause of the continual addition made to its length is 

 probably to be found in the growth of the madrepore in which it is sheltered, and which would 

 soon inclose the Magilus within its stony walls did not the mollusk provide against such a fate 

 by lengthening its shell and taking up its residence in the mouth. 



The most curious point, however, in the economy of the Magilus is, that, as fast as it adds 

 a new shell in front, it tills up the cavity behind with a solid concretion of shelly matter, very 

 hard, and of an almost crystalline structure, so as to leave about the same amount of space as 

 in the original shell. The animal is always to be found in the very front of the shelly tube, 

 ami closes the aperture with a strong operculum that effectually shields it against all foes. 



The color of the Magilus is whitish. Only one species is known. 



In the peculiar formation of the shell there is an evident analogy with the successive 

 chambers formed by the pearly nautilus. In both cases the animal is of small dimensions 

 when compared with the magnitude of its dwelling, and in both cases the creature continually 

 advances forward, taking up its residence in a chamber formed in the front of the shell, and, 

 closing the passage behind in proportion to its advance. The chief difference, however, 



