516 FOSSIL INVERTEBRATED ANIMALS. 



surface of an arbusculum, entirely calcareous, which is fixed 

 to its base ; ramified in an irregular manner, and pierced with 

 a great number of pores. This genus corresponds to the divi- 

 sion of the madrepores ramoscB of Gmelin. 



Such madrepores are not found in our seas, and have been 

 met with hitherto only in those of America and the East Indies, 

 where they especially abound. Fixed by their basis at very 

 considerable depths, they appear to develop themselves by 

 elevating, more or less, the foliaceous expansions, or caules- 

 cent ramifications, which constitute them. We are totally 

 ignorant of their modes of growth, of multiplication, and of 

 death. We only know that the polyparium, which is entirely 

 calcareous, is of a tissue so much the closer as it approaches 

 the parts which constitute its base ; and that, on the contrary, 

 the extremity of the ramifications is always more porous. The 

 lower cellules are always more defaced, while the upper, and 

 the extremity of the branches, are often terminated by an exca- 

 vation tolerably profound. 



To the very rapid growth of the madrepores proper, and 

 especially that of the muricata, is attributed the formation of 

 the numerous reefs which exist in the Southern and Indian 

 Oceans, and in the Red Sea. Be this as it may, it is certain 

 that the majority of the islands, in those parts of the world, rest 

 on a calcareous soil, entirely composed of stony polyparia, and 

 that their most elevated mountains are formed of the same 

 material; but it would be difficult to ascertain that the madre- 

 pores are the species found there in the greatest number. 



The polypi of the madrepores, which are extremely common 

 in the seas of the hot climates, and principally in those of the 

 torrid zone, can no longer exist in the climate which we in- 

 habit. We find, however, the polyparia of these species in the 

 ancient strata, as well as in the more modern, of our countries, 

 where they have been formed ; but it appears that they were 

 not so abundant as in the seas where these polypi exist at the 

 present day : in proof of which we may cite the reefs and 



