said to be found in Carboniferous Rocks. 45 
figures last referred to seem to represent a fossil having some 
resemblance to the ribless varieties of C. Schlotheimi. 
a 
Lingula Credneri, Geinitz. 
All the merit in connection with the Carboniferous age of 
this species is due to Mr Kirkby; and I am ready to admit 
that the specimens which he has found in the coal-measures 
“at the Ryhope winning, near Sunderland,” belong to it.* 
I may be allowed, however, to retain some slight reservation, 
as it is well known that many species of Lingula, from 
widely separated formations, are with difficulty distinguished 
from each other. 
It would be a waste of time to go further into a discussion 
on the Permian species referred to in the previous pages, be- 
cause itis clear Mr Davidson and myself are not in agree- 
ment on first principles. His groups are more comprehensive 
than mine. Many groups, which I consider to be equal to 
genera or species, are regarded by Mr Davidson as mere sub- 
genera or sub-species. I have elsewhere stated my objections 
with reference to the latter view on genera;} I may now be 
permitted to make a few observations in the same sense with 
regard to species. 
(To be continued.) 
* When mentioning the localities of this species in my “ Monograph,” I 
added the following :—“ Professor Johnston informs me” (I received the infor- 
mation from him first verbally and afterwards by letter) “that he has pro- 
cured specimens of a Lingula in the underlying freestone (Rothe-todte-lie- 
gende) near Ferry Hill” (p. 84). Every one acquainted with the high scien- 
tific reputation of the author named, on reading the following remarks by Mr 
R. Howse, must have felt at least surprised. ‘‘ I may be allowed to question 
the occurrence of this or any other species of Lingula in the underlying red sand- 
stone, as stated in King’s ‘ Monograph’ on the authority of Professo Johnston, 
as this sandstone is a true coal-measure stratum” (An. Nat. Hist., 2d Series, vol. 
xix. p. 44). They will be gratified to learn, however, that not only may “ this 
or any other species of Lingula”’ occur, as stated in the “ Monograph,” but that 
specimens, identified by Mr Kirkby with Lingula Credneri, have actually been 
found by him in a “ true coal-measure stratum,” occurring at a depth of 951 feet 
below the surface! (Vide Quart. Jour. Geol. Soc., vol. vi. Part I. pp. 412, 413.) 
J Vide my Paper in “ Nat. Hist. Review,” vol. i. 
