242 SEAWEEDS 



branched forms of a brittle character. The geological 

 history of the family goes back to the Cretaceous 



FIG. 83. Lithothamnion polymorphum reduced. 



times, and forms have been described, but with less 

 certainty, from the early secondary rocks (Muschel- 

 kalk, Trias). They first appear, however, beyond 



