Among the genera of fern-like plants of Palæozoic Age there are a number which have orbicular or reniform leaflets. Detached leaflets of this form are frequently found, and it is a matter of difficulty to determine to which of several genera such fragments belong.
Under the name Cyclopteris Brongniart (1828, p. 215) described some orbicular leaflets found in Upper Carboniferous strata, and later investigators have shown that most of these leaflets were the basal or stipular pinnules (aphlebiæ) of the frond of the Pteridosperm Neuropteris. They were sessile on the rachis and had broad bases of attachment, while the shape of the pinnules on the upper parts of the frond was quite different. The Scottish fossils which will be described in this memoir are also orbicular leaflets and have been named Cyclopteris by some authors. There is evidence, however, that they were pedicillate and were not the aphlebiæ of the frond which bore them.