46 CLASS I.— ORDER I. 



STONY. 



8. F LVSTR A petrea. Foliaceous, fan-shaped, and 

 proliferous ; summits rounded ; cells alternate, co- 

 vered with small papillae, placed on two opposite 

 lines ; height from three to four centimetres. 



On the Thalassiophytes of Australasia. 



TREE-FORMED. 



9. Flustra frondiculosa. Arborescent ; divisions 

 obtuse, trichotomous, and crowded ; cells placed one 

 above the other. 



Indian Ocean. 



BRISTLY. 



10. Flustra hispida. Arborescent and spongy; 

 divisions branching ; stuck and surrounded with hairs. 



Mediterranean sea ; very scarce. 



VELVET. 



11. Flustra pilosa. Foliaceous or covering Thalas- 

 siophytes ; the under border of the cells with a bristly 

 tooth. 



European seas ; usually on the Thalassiophytes, 

 which it sometimes wholly covers, but does not in- 

 crustate. 



DOWNY. 



12. Flustra tomentosa. Incrustation, soft and 

 velvety ; cells scarcely visible. 



In the European seas, attached to Thalassiophytes 

 and Sertularias. 



linear. 



13. Flustra lineata. Incrustation ; cells situated 

 on transverse and oblique lines. 



