PLATE 17, 18, 
surrounding stone, and calcareous ; possessing all the nature 
of the original, of which they evidently formed a part. 
These bodies, when minutely examined, are found to have 
the same radiated structure as the dissepiments, which in 
many parts of the fossil appear to have surrounded the tubes 
in a solid form, instead of being divided by intervals into 
plates or laminaa. A similar structure sometimes takes place 
in the Madrepora musicalis. 
It is necessary also to remark in the present specimen an 
appearance of perpendicular dissepiments. These, however> 
though connected with the transverse ones, do not seem to 
have constituted any part of the original coral : but, appar- 
ently, have been formed since its mutation, by a gradual 
deposition of siliceous matter, between the tubes. 
