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 concentrka. 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. 



