Upper Devonian Placoderms of Ohio. — Claypole. 359 
the Salina with beds of rock salt intervene and are at least 
1,000 feet in mass. In these were found the shields of 
Palceaspis in great numbers. They are consequently of equal 
age, to say the least, with the pteraspids of the Ludlow, all 
the yet known specimens of which except one solitary shield 
of Cyathaspis (Scaphaspis) ludensis have come from the up- 
per division. 
This discovery enables us to trace the genealogical tree a 
little nearer to its root, but even this does not bring us quite to 
the point where the clue is completely lost, for in a hard but 
thin sandstone bed considerably deeper down the writer soon 
afterward found crushed, broken and incomplete specimens of 
ichthyic organisms which enabled him to carry the history 
of the vertebrates almost to the base of the (Upper) Silurian 
system. The sandstone in question lies toward the base of 
the Clinton rocks and hence the fossils are older than those 
last mentioned by all the time represented by the base of the 
Salina, the whole of the Niagara and most of the Clinton, or 
at least 1,000 feet of deposit in the region where they occur. 
Some of them show the peculiar markings of the pteraspidian 
shield and are accompanied by numerous pellets of phosphatic 
matter, seemingly coprolitic, which lend further confirmation 
to the discovery. These afford indications of elasmobranch 
fishes. 
Lindstrom has recently carried the history of the pteras- 
pidians in Europe to an earlier date by his description of a 
Cyathaspis from the island of Gotland found in a stratum 
whose nearest equivalent is the English Wenlock shale. His 
paper in the Annals of the Royal Swedish Academy appeared 
after this article was written. By this discovery the Sweden 
pteraspidians are carried back to an earlier date than any \ ci 
found in England.* 
*Two claims are made for the discovery of ichthyic remains in strata 
of yet older date. Rohon of Prague has described some fossils as fish- 
teeth which were found in the glauconite sands of St. Petersburg!) 
assigned in general to the Ordovician (Lower Silurian) era. The writer 
has not yet seen his paper and can therefore form no opinion upon the 
evidence. Walcott in 1891 announced the presence of fish fossils in 
strata of similar age in ( !olorado. lint the evidence from stratigraph.3 
is far from conclusive and the specimens to the paleontologist are 
strongly suggestive of Upper Devonian affinity and age. 
