506 The Geological Museum of the School of Mines, [August, 
that separate the Silurian from the Devonian fossils represent in 
reality an immense lapse of time, during which the fauna of the 
world underwent great changes. We will not say that all the old 
forms of life were exterminated and new beings created to take 
their places, nor can we prove that during these unknown ages 
the laws of development were slowly changing the plastic organ- 
isms into new forms better adapted to meet the altered conditions 
under which they were forced to live. We can only say that the 
record is broken: to-morrow the missing chapters may-be discov- 
ered and new light thrown upon the enigma, but to-day we must 
pass it by. But while most of the fossils of the Devonian differ 
in genera and species from those of the older fauna, yet they 
belong to the same families and orders, with the exception, of 
course, of the fishes, which are new to the life of the world. The 
corals, mollusks, and crustaceans are present in great numbers, 
and in a general way resemble their representatives in the Silu- 
rian, but on the whole they present greater diversity and indicate 
more advanced conditions. The presence of corals in the rocks 
of this age in what are now the Arctic regions indicates that there 
was little diversity of climate at the time these animals were alive. 
The fossils which particularly attract the attention in these 
cases, and which will always be a center of interest to the student 
of the Devonian, are the remains of fishes, of which this collec- 
tion contains a grand display that is unrivaled by any other 
museum in this country. Many of these fossils are unique, and 
in some instances are the only specimens of their kind known; 
many of them being the types figured by Prof. Newberry in the 
Geological Reports of Ohio, Among the first objects to attract 
the attention are the great sword-shaped spines which are the 
type-specimens of the genus Macheracanthus; these highly- 
polished spines, some of which are twenty inches in length, 
are samples of the weapons worn by the old Devonian sharks. 
These ancient fish-spines illustrate the economy that is shown in 
so many of nature’s works, in gaining great strength with the use 
of the smallest possible amount of material. Here also are the type- 
specimens of the genera Acanthaspis and Acantholepis, which show 
a strange combination of plate and spine that is unknown in mod- 
ern fishes. Another slab of limestone shows the head of an old 
Devonian fish that measures seven or eight inches in length. The 
head of this fish was Agee encased with solid bony plates t that — 
