reproduction; evolution 301 



The type of structure found in Diplopora (Fig. 181) was also 

 shown by many other forms from the Middle Triassic. It was a few 

 centimetres long and bush-like in appearance, the main stem, 

 which sometimes had a club-shaped apex, being covered with 

 whorls of branches that arose in groups of four, each bearing 

 secondary branches which terminated in hairs. In the older thalli 

 the outer part of the branch dropped off leaving a scar on the cal- 

 careous shell. The sporangia are reported to have been modified 

 branches. Diplopora is a widespread genus from the Triassic rocks 

 of the eastern Alps, Germany and Siberia. 



Palaeodasycladus (Fig. 182), from the Lower Jurassic, bears a 

 resemblance to the Uving species of Dasycladus. Near the base 

 there were only primary branches, whilst higher up secondary and 

 tertiary branches were to be found. 



Fossil forms, practically identical with living species of Cymo- 

 polia, Neomerts and Acicularia have been found in all the recent 

 strata from the Eocene upwards. 



Charophyceae 



Lagynophora, a genus from the Lower Eocene, can be ascribed 

 to this group, whilst Palaeonitella (Fig. 183), from the Middle 

 Devonian, may belong here also although its affinities are not so 

 clear. Gyrogonites and Kosmogyra are names which have been given 

 to oogonial structures which closely resemble those of Chara, and 

 which are very abundant in the Lower Tertiary beds of England 

 and elsewhere. Throughout their history there has been a tendency 

 for simplification and reduction of parts. 



Fig. 183 Charales. Palaeonitella cranii ( x 124). (After Hirmer.) 



