Note AZ — Chapter XII
Reading edition
"Upwards of eight hundred extinct species of animals have been described as belonging to the earliest, or Protozoic and Silurian period, and of these only about one hundred are found also in the overlying Devonian series; while but fifteen are common to the whole Palæozoic period, and not one extends beyond it."—(M. de Verneuil and Count D'Archiac, quoted by Mr. D. T. Ansted. 1844.)