172 THALLOPHYTA. [CH. 



Verticillatae. A brief description of a few genera from different 

 geological horizons must suffice to draw attention to the 

 character of the data for a phylogenetic history of this group. 



The fossil examples of the genus Cymopolia {Polytrypa) 

 were originally described by Defrance^ 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^ 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 harhata. The two drawings of Cymopolia reproduced 

 in fig. 33, A and B, have been copied from Munier-Chalmas' 

 note in the Comptes Rendus^; 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^ 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. 



Vermipo7'ella. 



This generic name was proposed by Stolley for certain 

 branched and curved tubes found in Silurian boulders from the 



1 Defiance (26) p. 453. 2 Munier-Chalmas (77) p. 815. 



2 Munier-Chalmas ihid. ^ Defrance (26) PI. xlviii. fig. 1. 



