pression on the surface which joins the pentagonal base of the en- 

 crinite. 



From the peculiar nature of the articulation of the vertebras of the 

 whole column, the crenated edges being exactly fitted to each other, al- 

 most in the manner of a dove-tail joint, it is obvious that no rotatory 

 motion could have been performed. It is also evident, that as the 

 motion admitted is that which accompanies the sinking in of the 

 teeth of the articulation into the notches of one side, and the raising 

 them out of the other, as may be seen in the specimen, Plate XIII. 

 Fig. 8, it can only be in a lateral direction ; but from the circular 

 arrangement of the crenated surface of articulation, it is plain that 

 the animal would possess the power of bending laterally, with equal 

 facility, in any direction, and would thereby enjoy all the advantages 

 of a rotatory power, without the insecurity with which that might 

 have been attended. It is, indeed, true, that as the motion must be 

 regulated by the depth of the crenated edge, and the thickness of the 

 intervening ligament, the quantity of motion depending on each 

 joint, must have been very small ; but when it is considered that all 

 the neighbouring joints, and, perhaps, those of almost the whole co- 

 lumn, would partake of this motion, it will be evident, that in so 

 long a trunk as this animal may be supposed to have possessed, the 

 power of flexion must have been very considerable. 



But in almost every other animal, a greater degree of mobility is 

 given to the vertebral C9lumn, as it approaches to the head, or to that 

 part of the animal which is intended to seize and receive its prey ; 

 so in this animal a corresponding modification of the articulating sur- 

 faces of the vertebrae nearest to the body of the animal, will be found 

 to exist. 



In every specimen of the . vertebral column of the lily encrinite 

 which I have seen attached to the superior part of the animal, that 

 part of the column next to the pelvis has been thus composed of 



