Those genera, like Paradoxides, Olenus, Asaphus, Phillipsia and others, in which this groove cuts the posterior edge of the head-shield on the inner side of its angle are referred to the Opisthoparia; those, like Dalmanites and Phacops, in which it cuts the lateral border in front of the posterior angle, belong to the Proparia.
Thus we have a Lower Cambrian with Olenellus, a middle series with Paradoxides and an Upper Cambrian with Olenus.
An uppermost series lies above the Olenus fauna in some areas; it is represented by the Tremadoc beds in Britain or by the Dictyonema beds or Euloma-Niobe fauna elsewhere.
On the North American continent, as in Europe, the Cambrian system is divisible into three series: (i) the lower or "Georgian," with Olenellus fauna; (2) the middle or "Acadian," with Paradoxides or Dikelocephalus fauna; (3) the upper or "Potsdam," with Olenus fauna (with Saratogan or St Croix as synonyms for Potsdam).
Limestones and shales with the Euloma-Niobe fauna come at the top. The upper series (Olenus) has been minutely zoned by W.
Above the fucoidal sandstone an important break appears in the system, for the Paradoxides and Olenus divisions are absent.
Another myth has it to be Olenus, a son of Hephaestus, and father of Aega and Helice, two nymphs who nursed Zeus.
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