THE OLD RED SANDSTONE FISHES OF ENGLAND. 
447 
some of the fins. But there is still much to he found out 
with regard to these curious fishes. There are several 
species of Pteraspis : one from the cornstones of Hereford- 
shire, the Pteraspis rostratus, which is somewhat abundant, 
retains the name given by Agassiz. There are two or three 
other species met with in the Devonian strata, one being 
from Germany obtained in the neighbourhood of the Laache 
See. In the upper Silurian beds three species occur — 
Pteraspis truncatus , Banksii , and Ludensis — the latter being 
obtained in the lower Ludlow strata, and as yet the oldest 
fish that is known. In the vast thickness of rocks which 
underlie the upper Silurian strata, no one can tell what remark- 
able fish yet wait to be discovered. At present the members 
of the little group which we have just described, are the most 
ancient vertebrated denizens of the globe which geological 
science has brought to light. It can hardly be that no 
nearer approach to the lower forms of animal life existed in 
still earlier times, to connect these somewhat highly organised 
fish with the invertebrate class. Ere long we may have to 
describe still older and still more remarkable fish, which we 
trust will fill up some of those gaps, or represent some of 
those missing links which it is the geologist's duty patiently 
and perseveringly to seek. 
