In his recently published excellent Memoir on the “Fauna of the Lower Cambrian or Olenellus Zone,” Mr. Walcott has referred briefly to the presence of the fauna in Wales. The following additional facts bearing on the question may therefore be of some interest, and they will, I think, show that there is strong evidence in favour of the conclusion arrived at, that the Olenellus fauna occurs in the Caerfai Group of St. Davids, and in beds at the same horizon in North Wales.