The fossil examples of the genus _Cymopolia_ (_Polytrypa_) were originally described by Defrance[317] in the _Dictionnaire des Sciences Naturelles_ as small polyps under the generic name _Polytrypa_. In the Eocene sands of the Paris basin there have been found numerous specimens of short, calcareous tubes which Munier-Chalmas has shewn are no doubt the isolated segments of an alga practically identical with the recent _Cymopolia_. A section[318] through one of the fossil segments presents precisely the same features as those which are represented in fig. 33, A. The habit of the Eocene alga and its minute structure were apparently almost identical with those of the recent species, _Cymopolia barbata_. The two drawings of _Cymopolia_ reproduced in fig. 33, A and B, have been copied from Munier-Chalmas’ note in the _Comptes Rendus_[319]; the corresponding figures given by this author of the Eocene species (_Cymopolia elongata_ Deb.) are practically identical with figs. A and B, and show no points of real difference. The segments of the thallus of the fossil species, as figured by Defrance[320], appear to be rather longer than those of the recent species. The calcareous investment of the axial cell of the thallus was traversed by regular verticils of branches or ‘leaves’; the central branch of each whorl terminates in an oval sporangial cavity, exactly as in fig. 33, A and B; and from the top of this branch there is given off a ring of slender prolongations which terminate on the surface of the calcareous tube as regularly disposed depressions, which were no doubt originally occupied by their swollen distal ends as in the recent species. _Vermiporella._ This generic name was proposed by Stolley for certain branched and curved tubes found in Silurian boulders from the North German drift[321]. The tubes have a diameter of ·5–1 mm., and are perforated by radial canals which probably mark the position of verticils of branches given off at right angles to the central axis. The surface of the tubes is divided into regular hexagonal areas. The resemblance of these Silurian fossils to _Diplopora_ and other genera favours their inclusion in the Verticillate Siphoneae. _Sycidium._ Fig. 32, B. The fossils included in this genus were first described by Sandberger from the middle Devonian rocks of the Eifel, and referred by him to the animal kingdom. More recently Deecke has suggested the removal of the genus to the calcareous Siphoneae, and such a view appears perfectly reasonable, although without more data it is not possible to speak with absolute certainty.