298 THE ALGAE 



far more important than its present living representatives. The 

 various forms are all based on a type of construction which can be 

 sufficiently explained by descriptions of a few of the more repre- 

 sentative types. 



Fig. 178 Dasycladaceae. Rhabdoporella pachyderma ( x 135). 



(After Hirmer.) 



Rhabdoporella (Fig. 178) seems to be one of the most primitive 

 genera as it is represented by a purely cyUndrical shell that is 

 studded with pores through which the threads passed. It is known 

 from the Ordovician and Silurian. 



Fig. 179 Dasycladaceae. Cyclocrinus porosus ( x 8). (After Hirmer.) 



