LECTURES ON MOLLUSCA. 27 



proper, the animal, as it increases in size, periodically produces beau- 

 tiful foliations or varices from its mantle, at least three on each whirl. 

 In the typical species these are thin, light, and armed with numerous, 

 often very long spines; and the canal which holds the breathing 

 siphon is greatly produced, nearly closed, and also armed with spines. 

 One would think the animal would be as much incommoded by its 

 splendid dress as a fashionable lady in a crowded ball-room. As the 

 the animal grows, it eats away the last year's varix, which would 

 otherwise close up the aperture. It often happens that old mollusks, 

 either to lighten the weight they have to carry on their backs, or from 

 becoming more portly inside, eat out part or the whole of the interior 

 partitions in the same way. If the spire is long, or they are attacked 

 by borers in the upper region, where the liver works, they also have 

 the power of partitioning off the unused or diseased part by septa, 

 which, however, are not regular or perforated as in the Nautili. 



When the shells are strong, and the varices numerous and foliated,, 

 they are called Phyllonotus. They are very numerous and beautiful 

 on the west coasts of tropical America and Africa. The shells of 

 Pteronotus have a few wing-like varices. When these are feebly 

 developed, as in Muricidea, they pass into the next genus, Trophon, 

 where the varices have degenerated into m.ere raised lamina. This is 

 an arctic form, both of the northern and southern seas. The Typhis, 

 which appears first in the older Tertiaries, is a Murex with a single 

 open spine between the varices. This is supposed to perform the 

 function of an excurrent canal, like the slit in Pleurotoma, or the hole 

 in Vissurella. Another group, of which the Spindle-shells are the 

 type, has no varices at all ; but both the spire and canal are greatly 

 elongated. The true Fusus is a tropical form; but an intermediate 

 group, with moderate canal, (Chrysodomus,) abounds in the arctic seas. 

 The Chrysodomus antiquus, still common in the British seas, and found 

 in the whole circumpolar region of the North, was equally common in 

 the various tertiary epochs of the English Crag. A reversed variety 

 ( r * Fusus contrarius") was the characteristic species of the Ked Crag, 

 and is now found living, beyond the limits of the normal form, in the 

 Mediterranean and on the cost of Spain. The Scotch call it the 

 " roaring buckie," from the " sound of the sea " which the air makes 

 along the spiral passages when held to the ear. The Zetlanders hang 

 it flat, put a wick in the canal and oil in the body whirl,, and make a 

 lamp of it. It is now fashionable to suspend the great Turbo in the 

 same way as a flower vase. The Clavellas have curiously deformed 

 mouths, and abounded in the Eocene age. 



Lamarck, knowing little of the animals, divided his families accord- 

 ing to the length of the canal ; but this is no index to the length of the 

 siphon. In the Pisania group, the canal is very short, but the siphon 

 is moderately long and curled back over the shell in walking. A tooth 

 on the body whirl, marking off the top end of the mouth, shows the 

 position of the excurrent canal. The Enginas are little shells with 

 wry mouths, about which very little is known, though they are very 

 common on both shores of tropical America. 



AM Pisania represents in this family Lamarck's Purpurids, so Comi- 

 nella and Metula represent his Buccinids. They are in fact Buccinums 



