70 



that, of a more extended surface : and thus, by a continuance of these 

 labours, on an increasing scale, the turbinated form has been produced. 



This madrepore, like the former, passes into several varieties, de- 

 pending on the direction given to the tubuli bj different circum- 

 stances. Thus in the fossil here depicted, a conoid form is produced 

 by the labours of the madreporean insect having been directed in a 

 more perpendicular direction than in the former coral. Traces of this 

 species of coral is sometimes detected in silicious pebbles : yielding 

 an additional proof of the great antiquity of their formation. 



A corallite of the discoid kind was suspended in muriatic acid much 

 diluted, which, by removing the calcareous earth, soon exposed the 

 flocculent membranes of the madrepore. But, in this instance, the mem- 

 branous flocculae were exceedingly small, hanging but a very little way 

 below the edge of the coral ; and, on the least agitation of the glass, 

 innumerable minute portions of membranes became detached, and 

 slowly sank to the bottom of the glass. The smallness of the pieces of 

 membrane might be here probably accounted for, by the structure of 

 the madreporite which they composed ; since being of the species de- 

 lineated, Fig. 4 and 5, it must be obvious, that, from the multitude of 

 pores with which it is pierced, the membrane must suffer such frequent 

 inflection as would give very little reason to expect that, in a corroded 

 preparation, of even the recent madrepore, any thing like the form of 

 the madrepore could be preserved. The circumstance of these mem- 

 branous flocculi appearing to possess a greater degree of gravity than 

 belongs to animal membrane in general, may be accounted for, by 

 considering that they may yet retain some particles of earth in some 

 of their cavities, which are defended from the action of the acid, 

 by being completely inclosed in the membrane. 



The ramose madrepores, with distinct stars and tubercular porous 

 interstices next require our notice. Of these, it will not be possible 

 to exhibit many interesting specimens, in a mineralized state ; since, 

 from the small number of specimens which have been found, and 



