502 FOSSIL INVERTEBRATED ANIMALS. 



no proof that any change has been effected in the temperature 

 of the chmates which we inhabit. Bat the study of organic 

 fossil has clearly established that this temperature has been 

 lowered, or that beings, which cannot exist at the present day 

 but in regions much hotter than ours, were formerly capable of 

 existing in those where the winter would now destroy them. 



On this change of temperature we have already dilated, and 

 adduced what we conceive to be very adequate proofs in favour 

 of this opinion. Additional proofs are, however, to be gathered 

 from the study of fossil polyparia. 



We know that the seas of the northern regions support very 

 few of the genera of this family or order, and that they con- 

 tain none which are remarkable for size. It is not so with 

 those found in the fossil state in the same regions. Not only 

 are many very large specimens to be found there in the fossil 

 state, whose genera are no longer living but in the equinoctial 

 climates ; but an era has existed when the bottom of the sea, in 

 our part of the world, was literally covered with them. In the 

 department of Calvados, says M. de France, strata are ob- 

 served to a very great extent, which are scarcely composed of 

 anything but the debris of polyparia. In other regions, still 

 further north, there exist, in like manner, numerous remains of 

 polyparia in a fossil state, whose genera are at present con- 

 fined to the warmest latitudes of our globe. 



With the exception of the strata of lacustral formation, 

 which contain the debris of beings which belong evidently to 

 genera, and perhaps to species which live in our climates at 

 the present day, the others present us in general only the 

 remains of vegetables and animals, whose genera exist no 

 longer, but under a temperature much more elevated than 

 ours. 



The fossil astreseae, to which the name of Astraites has com- 

 monly been given, are found in strata anterior and posterior to 

 the chalk, and in the chalk itself 



Although the fossil species of this genus are numerous, it 



