Halimeda.
An example of an Eocene species of Halimeda has been recorded by Fuchs from Greifenstein under the name of Halimeda Saportae[293]. The impression has the form of a branched plant consisting of wedge-shaped or oval segments, and there is a close resemblance to the thallus of a recent Halimeda, e.g. H. gracilis Harv. It is not improbable that Fuchs’ determination is correct, but without more definite evidence than is afforded by a mere impression it is a little rash to make use of the recent generic name.
γ. Dasycladaceae.
In this family of Siphoneae are included a number of genera represented by species living in tropical and subtropical seas.
The thallus consists of an elongated axial cell fixed to the substratum by basal rhizoids, and bearing whorls of lateral appendages of limited growth which may be either simple or branched. Many of the lateral branches bear sporangia or spores. The thallus is in many species encrusted with carbonate of lime.
The two genera Acetabularia and Cymopolia may be briefly described as recent types which are represented by trustworthy fossil forms.
Fig. 34. Acetabularia mediterranea Lamx. From a specimen in the Cambridge Botanical Museum (nat. size).
Acetabularia. Figs. 33, I, and 34.
With the exception of A. mediterranea Lamx. (fig. 34) the few living species of this genus are confined to tropical seas.