328 NATURAL SCIENCE [November 
capable of appreciating the fossil and preserving it for study when 
discovered. 
The importance of remembering these considerations when 
speculating on biological subjects has recently been illustrated once 
more by the discovery of a new Upper Silurian fish-fauna in the 
south of Scotland. As already mentioned in Natural Science 
(vol, xiii, p. 157) this remarkable assemblage of fishes or fish-like 
organisms has been found by the Geological Survey at the top of 
the Silurian formations of Lanarkshire; and some preliminary 
notes by Dr Traquair announce that a complete memoir on the 
subject will shortly appear. Now, scattered and abraded fragments 
of similar organisms have been known for nearly sixty years in a 
thin stratum, termed the Ludlow Bone-bed, in the Upper Silurian of 
Herefordshire and adjoining counties. Fossils of the same kind 
have been collected for nearly half a century in an Upper Silurian 
limestone in the island of Oesel, in the Baltic Sea. Traces of them 
also occur in Galicia, Pennsylvania, and New Brunswick; and a 
few years ago similar fragments were sent to me by the Geological 
Survey of Canada from another locality in Newfoundland. How- 
ever, notwithstanding this proof of the very wide distribution of the 
late Silurian fish-fauna in question, we have had to wait for the 
accidental discovery of a thin stratum in Lanarkshire to obtain even 
a faint idea of the strange types of life represented by the familiar 
scales and other exoskeletal fragments. 
Although it is now nearly forty years since Darwin’s “ Origin 
of Species” first appeared, his lament at the hopelessness of testing 
all the principles of organic evolution by reference to the “ records 
of the rocks” might indeed be appropriately renewed at the present 
day. The discovery of new fossils in all parts of the world has pro- 
gressed at an astounding fate in the interval; and we are beginning 
to perceive feebly some of the laws which govern their succession 
and distribution. The biologist who is prone to glance through 
palaeontological text-books, however, and utilise them in his specula- 
tions, cannot be too frequently warned of the imperfection of our 
knowledge and the danger of trusting to negative evidence. 
To understand the importance of this warning at the end of 
nineteenth-century science, it is only necessary to consider the case 
of some of the most striking and philosophically valuable vertebrate 
animals, . 
Firstly, there is the remarkably early Devonian organism 
Palacospondylus gunni, frequently referred to in these pages. 
Whether it is a primaeval lamprey or not, it is the single known 
representative of its group, and implies the former existence of a 
great race of which we are acquainted with no other member. This 
fossil occurs in the Caithness flagstones, which were deposited in a 
