xxii 



PRELIMINARY OBSERVATIONS. 



tions, as in the nautilus. Some orthoceratites are two or more feet in 

 length : the animal contained in them must have been of vast size. 

 Orthoceratites are the most ancient of fossil chambered shells, and 

 are chiefly found in transition limestone. 



Fig. 9. The Belemnite is a taper straight shell with an internal 

 chambered cone. In some species there is no chambered cone. This 

 unchambered internal shell may have performed the same office as the 

 internal bone of the sepia officinalis, or cuttle-fish. It is deserving 

 notice, that the coat of the belemnite, when slightly burnt, yields the 

 odour of burnt horn, which tends to confirm the supposition that in- 

 ternal shells were corneous substances. 



Fig. 13. The Nummulite, (so called from its resemblence to a small 

 Roman coin) has nearly a flat or lenticular form. It has within it a 

 cavity, divided by partitions into numerous small cells, without a sy- 

 phon or sipliunculus ; part of the outside of the shell is removed in 

 the figure, to show the internal chambered structure. Whether the 

 animal belonged to the genus Sepia is not know. 



This little fossil forms entire calcareous hills and immense beds of 

 building stone in some countries. "It is of stone composed of these 

 shells that the Pyramids of Egypt are constructed." Cuvier, Regne 

 Animal. 



All the above genera of chambered shells, with the exception of the 

 Nautilus and Spirula, are fossil. 



We are come now to other orders of molluscous animals, whose 

 organization is less complex, and their powers of motion more limited, 

 than in the cephalopodes. These are the inhabitants of bivalve and 

 univalve shells. The first are called by Cuvier Acephalous, being 

 wnthout heads. Of these the oyster ofiers the most familiar example. 

 Most of the species are permanently attached to rocks, and have no 

 member to protrude beyond the shell. Those species of the oyster 

 family that are not attached permanently, can only move by driving 

 out the water, as they suddenly shut the valves of the shell. Species 

 of other genera of bivalves, though without heads, possess the power 

 of locomotion. 



Fig. 16. represents the animal and shell of a Bucardium. 



This animal puts out a triangular body, formed of two pipes or 

 tubes, separated and flat, but which becomes round as the water enters 

 by the lower tube, and goes out at the upper one. The tubes are sur- 

 rounded M^ith hairs. When the animal is disturbed, or hears a noise, 

 it throws out water to the distance of a foot. When it wishes to 

 change its quarters, it protrudes a long foot, and seeks, with the further 

 end of it, some object or point of support, to which it fixes it ; the 

 animal then draws back its shell about two inches at a time, till it has 

 attained or reached the spot where it desires to abide. Cuvier re- 

 gards one of the tubes as suited for respiration by the absorption of 

 water, and the other for its excretions. He further states, that bivalves 

 which have these tubes live buried in mud or sand. 



The animals inhabiting univalve shells are chiefly classed by Cuvier 

 as Gasteropodes, from their moving in their stomachs like snails. In 

 most species of univalves, the aninuil has a head with two eyes, and 

 a trunk resembling the trunk of an elephant ; with this trunk it seizes 

 its food; and in some species the trunk is used for piercing other shells. 

 The animal crawls upon a fleshy foot, near the end of which there is 



