Fossil Graptolithus. 359 



remains to this day a knotty question, and it has been recently 

 suggested by an American naturalist, that it may have had a 

 vegetable origin, while I will venture to cut the gordian knot and 

 consider it to be nothing more nor less than the serrated spine of the 

 Raja pastinaca, or an allied species, at least the figure in Ly ell's 

 El. Geol. of the Graptolithus foliaceous bears a striking similitude 

 to one ; indeed the resemblance is so strong, that it is impossible 

 to fail observing the connection or relationship subsisting between 

 them, though I am aware my own view is opposed to the fact 

 established by Dr. Buckland in the Bridgewater Treatise, that 

 no fossil Kays have been detected in any stratum below Lias, con- 

 sequently excluding them altogether from the Mudstones of the 

 Silurian formation, where they are otherwise most expected as being 

 their natural habitat whilst living. 



But in doing so I believe I only add an ichthyodorulite of the 

 tail of a Bay, to those of the numerous cartilaginous sauroid fishes 

 of the older rocks. Mr. Orlebar is unable to afford me any light on 

 this subject, and I shall be glad to obtain a well preserved specimen,* 

 however small, of this fossil for microscopic examination of its inter- 

 nal structure for the sake of comparison with that of the spine so 

 abundantly found on the beach of our coast. Well may the Prionitus 

 be classed, as it actually is at present, among genera incerta sedis. 



I find the discussion going on in the newspapers relative to Mr. 

 Orlebar' s antediluvian ocean extremely inviting, as the existence of 

 such a sea (but at a period long anterior to Mosaic creation) may be 

 deduced from well-known data and explained on other theories, par- 

 ticularly on an hypothesis which I have had for years now under 

 review, or been endeavouring to model, as best calculated to illustrate 

 on more general principles, a good many of our geological facts. 



We have a few curious shells here possibly undescribed, and 

 of which I shall shortly send you lithographed figures, together 

 with some observations respecting the formation of the Diamond, 

 much at variance as they may be with received opinions. 



* Mr. Ansted has been applied to for one. 

 Note. — They are numerous smongst the fossils of the raised beaches on 

 the face of the Khasyah mountains, where they certainly do not, so far as I 

 can remember them, present any relation to spines or crustaceous animals, 

 such at least as we are now acquainted with, although their resemblance to 

 Pennatula is sufficiently striking. — Ed. 



3 A 



