205 
ing so very materially from every other species of trochital vertebrae. 
Like other entrochi, it is of a cylindrical form, but is somewhat 
flattened, and, most probably, by compression. The vertebrae of which 
it is composed are extremely thin in proportion to their width, being 
scarcely an eighth of an inch in thickness, although upwards of an inch 
in their medium diameter ; every vertebra being most thickly, and at 
the same time irregularly, beset with very small holes. In consequence 
of the exceedingly fine striae on their surfaces, the lines of articulation 
are so very fine, as hardly to be visible, except the eye receives the 
aid of a magnifier ; when it is discovered that the notches in the 
lines of articulation are so small, as to have the appearance of being- 
very finely serrated. The direction, too, of the articulation, is also 
very uncommon, being irregularly undulating ; this irregularity evi- 
dently proceeding, not from any modification of their form, from any 
circumstance attendant on the change from the animal to the mineral 
kingdom ; but certainly from a concurrence of arrangement with the 
minute openings which have been just particularized. Hence it is to 
be seen that the line which marks the articulating surface takes the 
middle of the intervening spaces between these openings, so as somer 
times to include one, and sometimes two rows of the openings, falling in 
with, and exactly adapting itself to, their irregular disposition. 
This specimen also formed a part of Mr. Strangers museum ; but of 
where it was obtained from, I have no information ; its close agreement, 
however, with some specimens, of which 1 shall presently speak, seems 
to determine, almost decidedly, on its having been obtained from the 
Isle of Gothland. 
The fossil Plate XV. Fig. 8, accords so nearly with the pre- 
ceding, as to render many of the observations which I shall now make 
applicable to both. Like the former, this specimen is composed of 
very thin trochitae, which are connected by the articulation of their 
very minutely serrated edges. In this the small openings are disposed 
with much more regularity than in the former specimen, they being 
