G. FLUSTRA. 
47 
On the Delesseria Palmata, and other marine plants 
of the European seas. 
COMPRESSED. 
14. Flustra impressa. Stony, and membranous ; 
cells nearly rhomboidal, obliquely compressed. 
Hab. .... 
MEMBRANOUS. 
15. Flustra membranacea . Incrustation; cells 
quadrangular oblongs. 
On the fucus of the Baltic sea. 
PAPYRACEOUS. 
16. Flustra papyracea. Frondescent, wedge- 
shaped, with many clefts ; cells rhomboidal oblongs, 
with the summits helmet- shaped. 
Mediterranean. 
CONCENTRIC. 
17. Flustra concentrica. Incrustation ; cells 
placed on concentric lines ; openings small, irregular 
and rounded. 
On the fucus of Australasia. 
PEARLY. 
18. Flustra baccata . Incrustation; cells long 
and gibbous ; openings very small. 
On the under surface of some marine plants of 
Australasia and the Antilles. 
tubular. 
19. Flustra tubulosa. Incrustation; cells simple. 
