306 Dr. W.B. Carpenter on Rhynchonella Geinitziana. 
XXXV.—On Rhynchonella Geinitziana. 
By W. B. Carventer, M.D., F.R.S., F.LS., F.GS. 
To the Editors of the Annals of Natural History. 
University of London, 
Burlington House, W. 
If Prof. King had contented himself, in his last communica- 
tion, with stating the facts which had come under his observa- 
tion in regard to the structure of Rhynchonella Geinitziana, I 
should have left it to your readers to judge whether that state- 
ment (to which I take no exception) at all invalidates the facts 
adduced by myself. For it must be obvious to any one accus- 
tomed to estimate the relative value of positive and negative 
evidence, that the existence of a single specimen of that shell 
possessing an outer layer not perforated by canals is of more 
weight than that of a dozen specimens in which the canals pass 
through what seems to be the whole thickness of the shell; since 
every paleontologist knows that the superficial layers of shells, 
especially Brachiopods, have been so frequently removed by 
abrasion previously to their fossilization, that in many forma- 
tions a perfect shell is a rarity. 
But Prof. King, without having seen my preparations, persis- 
tently refuses to admit the existence of such a specimen, and 
disposes of the facts which I have stated in regard to it by 
imputing to me incapacity as a microscopic observer. I am 
unable, according to him, to distinguish, in a vertical section, 
between canals which really stop short and canals which pass 
out of the plane of section ; and, in a tangential section, I have 
mistaken canals filled by transparent infiltration for the proper 
substance of the shell, which J affirm to be really continuous where 
he says that it ought to show perforations. As a microscopist of 
thirty years’ experience, as the original discoverer of the canali- 
cular structure in Brachiopods, and as the maker of several 
hundred preparations illustrative of that structure, I venture to 
ask whether it is more likely that I am deceived by such ¢rans- 
parent fallacies, or that Prof. King’s observations have been 
made upon abraded shells. And I believe that such of your 
readers as may have followed this discussion will agree with me 
that, so far from the “ clear evidence” adduced in Prof. King’s 
paper being entitled to acceptance ‘as entirely removing all 
doubts on the matter,” it leaves this matter precisely where it 
was before. 
The course which Prof. King has thought proper to follow in 
his revival of this discussion is in perfect accordance with that 
which he has adopted in recently controverting my statement of 
the existence of finely tubular Nummuline shell-structure in 
GENTLEMEN, 
