POTERIOCRIMUJ: ICXTRACRINUS. 103 



retiring angles ol' the colunni, and their great flexibility enabled them to expand on every 

 side and assist to poise the body of the animal in equilibrio, to move laterally, or to 

 hold fast to extraneous objects and thus remain unmoved by the current, or as Dr. 

 Buckland has observed, " they would close and fold themselves along the column in 

 a position which would expose the least possible surface to the element, and together 

 with the column and arms, would yield to the direction of the current." 



The manner in which the side arms are arranged around the colunm is well 

 exhibited in some of the figures represented in the beautiful group which constitutes 

 our first plate of illustrations, and in PI. 12, fig. 1, a. 



The Root or Base of Attachment. — Dr. Buckland in his Bridgewater Treatise 

 axlvances the idea that the root of the Briarean E.vtracrinus was slight and capable of 

 being withdrawn from its attachment. This suggestion, which we are neither prepared 

 to oppose or confinn, is founded on the circimistance that none of those solid secretions 

 by which the Ap'iocrlnes are known to have been attached to the sea bottom, have 

 yet been discovered in relation with the Briareus. This it is true is but negative 

 evidence as to the Extracrinus having possessed the power of locomotion, nor do we attach 

 much weight to it, as the same difficulty exists in regard to some of the carboniferous 

 limestone crinoids, whose base of attachment remains still undiscovered, but that they 

 were permanently fixed to the bed of the ocean by an indurated base cannot be doubted. 



The fact that great numbers of these fossil animals are frequently found in contact 

 witli masses of drifted wood which has been partially converted into jet gives strength 

 to the supposition that the Extracrinus Briareus often attached itself to floating pieces 

 of wood in the same manner as the living Aiiatifera is attached to drift timber in the 

 recent seas. It is also probable that the Briareus was often attached to the bottom in 

 situations where it was sufficiently finn, and the water clear and tranquil. 



The facts which give countenance to the opinion that the Extracrini were frequently 

 attached to floating timber are chiefly derived from the position the fossils occupy in 

 relation to a thin seam of lignite in the lias marl, between Lyme and Charmouth. 

 Dr. Buckland's observations on this part of our subject are so much to the purpose that 

 we are induced to transfer them to our pages. 



" Throughout nearly its whole extent, Miss Anning has constantly obsen'ed in this 

 lignite the following curious appearances : — The lower surface only is covered by a 

 stratum, entirely composed of Pentacrinites, and varying from one to three inches in 

 thickness ; they lie nearly in a horizontal position, with the foot stalks uppermost, next 

 to the lignite. The greater number of these Pentticrinites are presened in such high 

 perfection, that they must have been buried in the clay that now invests them before 

 decomposition of their bodies had taken place. It is not uuconnnon to find large slabs 



