MADREPORES. 



I8l 



pores ; they are inhabitants of the tropical and semi-tropical portions 

 of the great oceans, where they are found in a great variety of forms, 

 which has led to its subdivision into two great divisions consisting of 

 very many genera by Messrs. Milne-Edwards and J. Haime. The 

 animals are short, more or less cylindrical, witli a rounded mouth 



Fig. 65. — Meandrina cerebriformis (Lamarck). 



placed in the centre of a disc, covered with a few rather short ten- 

 tacula ; they form by their union a variously-shaped coral, which 

 often encrusts other bodies. 



The genus Aleafidrina differs from that of Astrea in having the 

 surface hollowed out into shallow sinuous elongated cells, furnished 

 on each side of the mesial line with crenulated lamellcC, the columella 

 is but little developed ; the polypidom, whicli, like all the group, is 



