FOSSIL INVERTEBRATED ANIMALS. 441 



contexture of which is analogous to that of the oyster, is pre- 

 served. An internal mould, petrified and free, is found in this 

 valve, but does not fill it altogether. A pretty large empty 

 space is /ound on one side ; and this space must necessarily 

 have been occupied by a body, or by a soluble portion of the 

 shell, which has disappeared after the petrifaction of the mould. 



The internal moulds of the spherulites, or of shells analogous 

 to them, are still more singular, in that, independently of two 

 considerable depressions which come forward in this mould, 

 there are two large holes which traverse it from one part to the 

 other. Some of these moulds are, as it were, foliated. It 

 would seem that the interval between each foliation must have 

 been filled by solid and soluble bodies, which have disappeared 

 since the petrifaction of the mould. Nothing that is known in 

 the living state can assist us in conceiving what may have been 

 the organization of animals which have left similar moulds 

 behind them. 



Neither do we know if the petrifaction which has seized these 

 bodies has been rapid. — We might suppose it to have been so, 

 on considering the moulds just mentioned — ^which might lead 

 us to believe that certain soft parts of the animals may have 

 been destroyed by it, or before it took place ; and that others, 

 such as more solid muscles, capable of resistance, have disap- 

 peared since : but it is very difficult to form satisfactory con- 

 jectures on this point. It appears certain, however, that in 

 some cases, relative to these moulds, the soft matter was insi- 

 nuated into, and petrified in, very narrow vacancies ; and that, 

 what surrounded them having disappeared, there remained very 

 slender laminae. 



The baculites have not been observed hitherto, except in 

 strata analogous to the chalk, or near that substance, and 

 where the testa has disappeared. Frequently the interior 

 moulds of their numerous partitions do not adhere one to 

 the other ; so that some portions of this singular shell, com- 

 posed sometimes of more than thirty of these moulds, which 



