175 
pression on the surface which joins the pentagonal base of the en- 
crinite. 
From the peculiar nature of the articulation of the vertebrae 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 column, 
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 pow^ of flexion must 
have been very considerable. 
But in almost every other animal, a greater degree of mobility is 
given to the vertebral column, 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 
