HOW TO KNOW THE SEAWEEDS 



81b Crusts thick, convoluted, spongy. Fig. 117. .Petrospongium rugosum 



Fig. 117. Petrospongium rugosum (Oka- 

 mura) Setchell & Gardner 



An entire plant showing the convoluted 

 appearance, X 1. Common on upper in- 

 tertidal rocks of central and southern Cali- 

 fornia. 

 Figure 1 1 7 



82a Thallus not erect, but sub-spherical, hemispherical, or expanded 

 and convoluted; surface smooth or warty 83 



82b Thallus not as above, erect 



85 



83a Thallus green, composed of macroscopic cells. Fig. 118 



Dictyosphaeria cavernosa 



B 



Figure 1 1 8 



Fig. 118. Dictyosphaeria cavernosa (Forskal) Borgesen 



A. Habit of an entire small plant with a portion cut out to show 

 the hollow character, X 3.2. B. Detail of several of the macroscopic 

 cells, X 12.8. 



Frequent on exposed rocks along the Florida coast. 



90 



