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Powrie to be the eggs of crustaceans, which is highly probable, for they have not only been found with Pterygotus anglicus in Forfarshire and Perthshire, but also in the Upper Silurian strata of England, in which species of the same genus, Pterygotus, occur.
Upper Old Red Sandstone in Scotland, with Fish and Plants. Middle Old Red Sandstone. Classification of the Ichthyolites of the Old Red, and their Relation to Living Types. Lower Old Red Sandstone, with Cephalaspis and Pterygotus. Marine or Devonian Type of Old Red Sandstone. Upper Devonian Rocks and Fossils. Middle. Lower. Eifel Limestone of Germany. Devonian of Russia.
BRITISH. Bituminous schists of Gamrie, Caithness, etc., with numerous fish. BRITISH. Arbroath paving-stones, with Cephalaspis and Pterygotus. FOREIGN. Oriskany sandstone of Western Canada and New York. BRITISH. Upper Ludlow formation, Downton sandstone, with bone-bed. FOREIGN. Niagara limestone, with Calymene, Homalonotus, etc. BRITISH. Bala and Caradoc beds.
The newest of the series is a clay-slate, on which, along the southern borders of the Grampians, the Lower Old Red, containing Cephalaspis Lyelli, Pterygotus Anglicus, and Parka decipiens, rests unconformably.
Besides some species of Pterygotus, several of the allied genus Eurypterus occur in the Lower Old Red Sandstone, and with them the remains of grass-like plants so abundant in Forfarshire and Kincardineshire as to be useful to the geologist by enabling him to identify the inferior strata at distant points.
Powrie enumerates no less than five genera of the family Acanthodidae, the spines, scales, and other remains of which have been detected in the grey flaggy sandstones. Pterygotus anglicus, Agassiz. Pterygotus anglicus, Agassiz. Forfarshire. Ventral aspect. Restored by H. Wodward, F.G.S. a. Carapace, showing the large sessile eyes at the anterior angles. b.
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