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Proceedings of the Eoyal Society of Edinburgh. [Sess. 
preserved in this particular case was an organic fragment in a state of 
putrefaction. The remains of the animal cells were discernible, as well as 
fragments of another micro-organism, which latter, however, was present in 
too small a quantity to make further investigation of its nature profitable. 
If we build up the organism from the evidence before us, we get a 
glimpse of a micro-organism that was very like our modern Actinomyces. 
The threads measured '75 /x to 1 /x across. They were too small to show 
any further indications of structure ; neither were there any indications of 
Fig. 17 . — Actinomyces a. x 1330. 
From Dunliath ferruginous limestone. Bits of thread covered with an irregular 
deposit of some coal-black substance. 
a. Part from which deposit has been removed, revealing underneath a 
portion of the minute threads that make up this micro-organism. 
h. The commencement of a branch. 
reproductive bodies of any kind. In virtue of the hyphal nature of the 
threads and their very small size, the only position that can be assigned to 
them is among the Actinomyces. So far as I am aware, there has been 
no previous record of a fossil micro-organism belonging to this group. 
Fossil Bacteria from the Cretaceous Bocks. 
General Revieiv of the Subject. 
(a) Whilst in one form or another a moderately large mass of know- 
ledge has been accumulated with regard to the fungi of the past, the 
information at our disposal with regard to fossil bacteria is very scanty. 
It seems necessary, in the first instance, to justify the position that it is 
possible to speak with some degree of certainty of the possibility of being 
able to recognise the remains of such small organisms as the bacteria. It 
is possible to recognise small fragments of animals or plants in fossiliferous 
stones, and their identification as such is never questioned. Such being 
the case, these organic fragments must have lain, in the majority of cases, 
on the ground or under water, and been subjected to the ravages of putre- 
