193 
tirely disappointed. In this whole mass, in which is a connected se- 
ries of vertebrae of nine inches in length, and which may fairly be 
extended to more than three times that length, by reckoning the dis- 
placed pieces which it is evident were once in continuation with it : in 
this mass, in which not half an inch is free from the vertebrae of this ^ 
animal, and in which it may be safely inferred, that some of the vertebral 
columns passed through the whole length of the slab, not the least trace 
of any regular termination can be discovered. Its examination, however, 
furnished the following facts : 
In this assemblage of vertebrae, which there is every reason to sup- 
pose must have belonged to one particular species of this animal only, 
a very considerable variety of form and of combination may be dis- 
covered : some being exactly the same size, forming a column uni- 
formly smooth and even ; some being alternately larger and smaller, 
forming a column with alternate risings and depressions ; some be- 
coming gradually larger, and then again contracting in size, and thereby 
acquiring a bulging form ; and others having regular articular de- 
pressions in their sides for the reception of lateral processes. Besides 
these, a great number of varieties are here observable, too many, indeed, 
to allow of being particularized ; and sufficient to shew that it would be 
rather difficult to detect the species of the animal by the form and 
appearance of the vertebrae. 
The general character of the trochitae of this species appears, how- 
ever, to be that they are pierced with a much larger foramen than 
that which is observable in the trochitae of other species. The trochite, 
Plate XIII. Fig. 29 , and Fig. 42, appear to have belonged to this spe- 
cies : as well as the silicious cast, Plate XIII. Fig. 10, and the casts 
existing in the mass of screw-stones formed of chert, and represented 
Plate XV. Fig. 6. 
In another slab from the same place I was, however, more success- 
ful, it containing that part of the skeleton of the body which has 
been called, in the stone lily, the pentagonal base. It, however, dif- ' 
fers essentially from the corresponding part in that species, as appears 
VOL. II. c c 
