FOSSIL INVERTEBRATED ANIMALS. 507 



bottom of the sea, at very considerable depths ; but we know 

 not if they are fixed there, though it appears very probable 

 that they are. It is to chance the discovery of the few speci- 

 mens existing in the collections of Europe is owing ; and they 

 came from the American seas. 



The fossil debris, belonging to this genus, are very common 

 in certain ancient strata. Their singular and varied forms have 

 caused them to be remarked by the ancient oryctographers, 

 who have given them the names of pentacrinos, lapis penta- 

 gonus, volvolcB, stellaria columellcBy asterice, cylindrita, &c. 

 They have also been called petrified sea-stars. The name of 

 entrochi has been given to inconsiderable portions of the stem 

 of these polyparia ; and that of trochi, to the articulations sepa- 

 rated from the entrochi. These stems are composed of pieces 

 placed one above the other, whose thickness varies, either 

 according to their position, or according to the species. The 

 great variety in these pieces, or articulations, seems to prove 

 the existence of a great number of species of this genus. They 

 may generally be divided into two parts — the one round, and 

 the other polygon : the first, furnish the thickest and the longest 

 pieces ; some are two inches in diameter, and others less thick 

 and more than three inches in length. It is clearly demon- 

 strated, by these specimens, that these stems have been adhe- 

 rent on other bodies ; as those of the gorgons, or other branched 

 polyparia ; and that several stems were often raised on the 

 same basis. The round stems are pierced, in the direction of 

 their axis, with a round hole, more or less wide, according to 

 the different species : that of some of them is smooth ; in others, 

 it is channelled circularly. Each articulation is marked, on its 

 two flat surfaces, with rays or striae, diverging from the centre 

 to the circumference. 



It is observable that the thickest stems have been clothed 

 successively, at their base, with layers which have enveloped 

 the primitive stem which supported the diverging rays. Al- 

 though on certain pieces of these thick stems we still find. 



