On Cyrtoma, a new genus of Fossil Echinida. 157 



They are placed at the head of the class called Radiata, 

 consisting of animals in which the several parts of the 

 body radiate as from a centre. It is in the Echinida that 

 we first perceive a tendency to that bilateral disposition 

 of the several parts of the body which characterises the 

 higher classes. Mr. MacLeay has observed that those who 

 attempt to form accurate ideas of animal life by studying 

 it only in the most complex shape, are like persons who 

 would penetrate the depths of Newtonian philosophy with- 

 out being previously acquainted with the simpler elements 

 of mathematical science. An intimate knowledge of the 

 structure and habits of the simplest form of animals is 

 indeed no less important to the physiologist than indispen- 

 sable to the geologist. 



The first is enabled to trace from them the progressive 

 development, and changes of organs according to their uses 

 in different classes of beings, while the second, by a familiar 

 acquaintance with the forms of the lower animals is enabled 

 to decypher and explain the nature and character of great 

 physical changes that have repeatedly altered not merely 

 the condition of the earth itself, but remodelled from time 

 to time the beings which have been placed upon it. Thus 

 it is that a knowledge of the fishes, the reptiles, mulluscs, 

 and polypes, the worms, and creeping things which are 

 regarded with indifference by the vulgar, is calculated 

 not only to enlarge the sphere of reason, but also to exercise 

 a powerful moral influence over the human mind by ren- 

 dering us better acquainted with the extent and beauties 

 of the creation, and the infinite power and goodness of 

 the Creator. 



It is not my intention to write a popular discourse on this 

 subject ; for it is one with which even the learned are as 

 yet but little acquainted, and the peculiar facts I am about 

 to detail are chiefly unknown even to them. It is there- 

 fore necessary to prepare the reader, as I have had to pre- 

 pare myself, by a consideration of the living forms which 



