40 Professor King on certain Species of Permian Shells 
son’s “ Monograph.” My opinions on these two species are 
unchanged ; so I cannot admit that either one or the other 
was common to both the Carboniferous and Permian periods. 
Spiriferina cristata, Schlotheim. 
It is stated in my “ Monograph,” p. 128, that this fossil 
“closely resembles one or more so-called species found in the 
Carboniferous and other formations, particularly the Sp. octo- 
plicata of J. Sowerby. Having examined in Mr J. de C. 
Sowerby’s collection the originals (from Derbyshire) of the 
figures in the ‘Mineral Conchology,’ the only difference I 
could perceive is, that they are wider than any examples 
which have occurred to me of the present species. Specimens 
bearing the name of Spirifera insculpta, in the Gilbertsonian 
collection of the British Museum, appear to be undistinguish- 
able from Sp. cristata. The Jurassic fossil which Zeiten 
has identified with the Sp. octoplicata is another closely 
analogous species.” I have also stated in the Introduction, 
p: xxi., that “ Sp. cristata is closely related to, if not iden- 
tical with, the Carboniferous Sp. octoplicata.” Mr Davidson, 
speaking of “‘a remarkable and unusually large individual 
obtained at Tunstall Hill by Mr Kirkby,” observes,—< So 
closely did this specimen resemble some of Mr Sowerby’s 
typical examples of the Carboniferous Sp. octoplicata, that it 
is very provable, if not entirely certain, that Sp. cristata is 
at most but a variety or race, slightly modified by time and 
circumstances, of the Carboniferous species. In the Permian 
period it was, however, in general a smaller shell, the number 
of ribs likewise frequently less numerous” (vide Mon. Brit. 
Perm. Brach., p. 18). And on a later occasion, describing ~ 
Sp. octoplicata, he says, “I am also still inclined to maintain 
the opinion expressed in my ‘ Monograph,’ namely, that the shell 
under description bears so close a resemblance to the Permian 
Sp. cristata of Schlotheim that it cannot be specifically sepa- 
rated, and could not in any case claim more than a varietal 
distinction” (vide Geologist, vol. ii. p. 21, Jan. 1860). Mr. 
Davidson, it will be seen, has advanced no more evidence than 
myself to prove that these Carboniferous and Permian fossils 
are specifically identical. 
