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 by different circumstances. 
Thus in the fossil here depicted, a conoid form is produced by the 
labours of the madroperean 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 addi- 
tional 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 
membranous 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 madi’eporite 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 paiticles 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 
