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 vertebras 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 articula- 

 tion 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 some- 

 times to include one, and sometimes two rows of the openings, fall- 

 ing in with, and exactly adapting itself to, their irregular disposition. 



This specimen also formed apart of Mr. Strange's museum; but of 

 where it was obtained from, I have no information ; its close agree- 

 ment, however, with some specimens, of which I 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 trochitse, 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 



