LETTER VI. 



MADREPORE MADREPORE AN POLYPE FOSSIL MADREPORE 



DIFFICULTY IN ASCERTAINING THE SPECIES TURBINATED 



MADREPORE. ...VARIETIES OF.. ..REMARKS ON ITS FORMATION. 



W E shall now proceed to the examination of the genus MADRE- 

 PORE, under which genus are placed all those corals, the cavities of 

 which are divided by lamellae disposed in a stellular form. 



The animal which in the recent coral fills these cavities, was first 

 depicted by Donati, in the forty-seventh volume of the Philosophical 

 Transactions, Page 105, Plate IV. and in the Natural History of the 

 Adriatic Sea, by the same Author. A correct copy of Donati's figures 

 are here given, since you will thereby be better enabled to judge of 

 the observations I may offer respecting the formation of some of these 

 fossil bodies which are next to be examined. 



The little polypous inhabitant of the madrepore, Plate II. Fig. 2, 

 3, 4, according to the concise but perspicuous description of Donati, 

 is composed of three different parts ; the feet, the shell, and the head. 

 The feet are in considerable number, and terminate externally in two 

 conical productions, which being placed on each side of every one of 

 the lamellae which give the stellular form to the cavity of the coral, 

 serve to affix the animal to the circumference of its cell, and may, 

 with propriety, be considered as the instruments by which the little 

 animal forms the lamellae themselves. The other end of these conical 

 productions unite and form round bodies, which possess somewhat of 

 the figure and of the properties of a muscle; they undoubtedly serving 

 to lengthen or shorten the feet, and also most probably to regulate the 



