2 
the paucity of fossil star-fish depends, either on some circumstance 
in the original composition of the animal, which renders it little fit to 
undergo the petrifying change ; or on some circumstance, in its mineral 
state, which prevents its preservation in its matrix, or its safe extri- 
cation from it. All these circumstances have, perhaps, some share in 
occasioning the scarcity of these fossils : it appears, however, to be 
chiefly attributable to the original conformation of the covering of 
the animal, which is the only part which can be preserved to us by 
mineralization. 
The coriaceous, and even pulpy consistence, of the coverings of these 
animals, in a living state, plainly evinces that the mucilaginous or 
membranous matter bears a very large proportion to the carbonate 
of lime, which enters into the composition of these bodies. On the 
cessation of life, therefore, a speedy decomposition of this animal 
matter must ensue ; and from a deficiency of earthy matter to 
support its form, the whole substance must, in general, be resolved 
into a shapeless mass. 
The crustaceous covering of one of these animals, of a smallish size, 
was found to be pierced with fifteen hundred and twenty apertures, 
through which passed, or to which were attached, as many horny 
tubes ; serving, according to M. Reaumur*, either as feet, or as organs 
through which the water received by the stomach of the animal was 
ejected. The anatomy of this animal, however, has not, at least to 
my knowledge, been pursued so far, as to determine the real use of 
these tubes, which seem rather to be analogous with the absorbent 
tubes of the echinus. For our present purpose, it is only necessary 
to remark, that the membranous matter connecting these tubes with 
the external crust, or lining the apertures through which these tubes 
pass, must considerably add to the quantity of animal membrane, on 
the predominance of which its perishable nature so much depends. 
* Observatio de Stellis marinis, Sect. viii. 
