FOSSIL INVERTEBRATED ANIMALS. 503 



is difficult, especially for those of the ancient strata, to seize 

 all their characters, or distinguish them all, in consequence of 

 their imparted state, or the destruction of the lamillae of their 

 stars ; or, finally, from the change of their substance into silex 

 or crystals. 



M. de France mentions two very curious specimens of this 

 genus in his possession. In one, the entire substance, as well 

 as a part of the lamellae contained in the stars, is converted 

 into a crystallization, which has preserved the form and con- 

 texture of the astraea ; in the other, a net-work of crystals, with 

 their points, but without any form of organization, has replaced 

 the matter which constituted the stars, which have remained 

 empty. It is difficult to conceive how a crystallization, which 

 appears to have been very tranquil, could have replaced the 

 matter of the cells of the polyparium, which are three or four 

 lines in diameter. 



M. de Lamarck, in his work on Invertebrated Animals, has 

 divided the species of this genus into two sections : in the one, 

 he has placed those whose stars are separated even from their 

 base ; and, in the other, those whose stars are contiguous. 

 But there are some intermediate species, which render this 

 division rather difficult of application. 



A considerable mass of the polyparium of the AstrcBa den- 

 dro'idea was recently discovered in the cliffs of Berneville, 

 department of Calvados, the description of which, in the Me- 

 moirs of the Royal Academy of Sciences of Caen, by its disco- 

 verer, M.Lesauvage, is worth inserting here. " This singular pro- 

 duction is formed of a considerable bundle of branching stems, 

 simply contiguous, from ten to fifteen lines in diameter, and 

 presenting, through their entire length, a tolerably regular 

 series of rounded dilatations and of circular contractions. The 

 branches terminate in blunt points at unequal heights ; and all 

 their surface is covered with lamellated stars, rounded, conti- 

 guous, and almost superficial. If we examine the transversal 

 section of a stem, we shall find that its interior is formed of 



