214 Miss Agnes Cranc — On Certain Living and Fossil Fisltes. 
in the Upper Silurian and Devonian rocks ; tlms it seems as though, 
unable to cope in the struggle for existence with the lighter-armed 
and raoreactive race of ganoids which predominated in the Devonian 
waters, they died out, leaving no iramediate descendants. The 
vertebral colurnn in the Placoderms was generally cartilaginous, a 
condition considered by sorne authors as indicative of a low Organi- 
zation, but as the quantity of hone composing their external sliields 
was mach greater than that forminsr the internal skeleton of the 
existing types of true bony fishes, and as traces of ossified caudal 
vertebrae liave been discovered in one genus, they ought rather to be 
highly placed in a systematic Classification. The group is considered 
by Professor Huxley to form a link between the Ganoids and the 
Teleosts, and as haviug most affinity with the living plated Siluroid 
Teleosts of the African rivers. 
Distribution and Hange of the Piscine Families in Geo- 
logical Time. — In considering the distribution and ränge of the 
various families in geological time, we find that authenticated remains 
of sharks, Placoderms, and Cephalaspids liave been obtained from the 
Lower Ludlow Beds of the Upper Silurian in Europe, but in 
America it is singulär that no fossil fishes liave as yet been discovered 
before the Devonian epoch, wdien the relics of numerous genera occur 
abundantly, differing, however, from the European forms. This 
dissimilarity in the fauna is probably owing to the differences 
existing in the physical geography of the two areas at the time 
of the deposition of the series. The Devonian formation is built up 
of freshwater, estuarine and marine strata, each group cliaracterized 
by its peculiar forms of life. In the Old Red Sandstone of Scotland 
and Russia, freshwater species predominate, while in the marine 
limestones of Devonshire, and the Eifel, Mollusca, Corals, and the 
remains of genera of inshore dwelliug fish indicate a shallower 
marine deposit. The greater part of the American Devonian, on the 
contrary, was apparently laid down in an open sea, and thus a 
monster marine fauna flourished, not so generally represented in 
Europe ; but it is interesting to note the identity of a few species 
occurring in localities where the beds are of similar structure to 
those of contemporaneous age in Europe. In both worlds the for- 
mation is alike distinguished by the great preponderance of ganoid 
over elasmobrancliiate fishes. The conditions existing during the 
formation of the Devonian rocks are well illustrated at the present 
day by the freshwater lakes, miglity rivers, and extended coast-line 
of the African and American continents, and it is a most suggestive 
and significant fact that the genera of living ganoid and dipnoid 
fishes most resembling the Palaeozoic forms are now, with two 
exceptions, found on those continents alone. Taking the various 
Orders of Professor Huxley’s comprehensive Classification in succes- 
ßion, we find that no traces of the first or lowest order, the Pharyn- 
gobranchii, which contains only the “ gullet-breathing ” Lancelet, 
liave been found in a fossil state. This is easily accounted for, 
however, by the soft and perishable structure of the species, of 
which no remains could possibly be preserved in the finest sedi- 
