242 SEAWEEDS 
branched forms of a brittle character. The geological 
history of the family goes back to the Cretaceous 
Fic. 83.—Lithothamnion polymorphum recuced. 
times, and forms have been described, but with less 
certainty, from the early secondary rocks (Muschel- 
kalk, Trias). They first appear, however, beyond 
