140 SEAWEEDS 
free or almost free from incrustation, while in others 
each filament is thickly incrusted. In the latter case 
they are constricted at short intervals like a string 
of beads. Penicillus mediterraneus has a growth- 
form formerly known as Espera mediterranea, in 
which there is no stalk, but all the filaments are 
free. Similarly the species of Avrainvillea with free 
Fic. 38.—Penicillus capitatus natural size. 
filaments and no stalk (A. comosa) were formerly 
placed in a separate genus Chlorodesmis. A fossil 
genus Orulites from the Eocene (Paris basin) has 
been placed here by Munier Chalmas, but though 
there is no doubt it is a calcified siphoneous Alga 
and does not belong to the Foraminifera as formerly 
thought, its position near Penicillus is not so certain. 
