52 CLASS I.— ORDER I. 



communicating together underneath, with one or more 

 bristly appendages on the outside, having their open- 

 ing generally on the same surface. They have no 

 distinct stem. 



PHERUSA. 



Fron DESCENT Polypidom with many clefts. Cells 

 oblong, projecting, and placed only on one surface ; 

 openings irregular. 



The Pherusas differ so materially from the Flus- 

 tras, that an eye the least exercised cannot pos- 

 sibly confound them with the numerous species of 

 that genus, nor with the Celleporas ; though, like 

 the latter, they have distinct projecting cells, but not 

 isolated like them, as the Pherusas communicate at 

 their base. They are equally removed from the Flus- 

 tras by the situation of their cells ; in this latter, when 

 the Polypidom is frondescent or foliated, the cells are 

 found on both surfaces ; in the Pherusa they are al- 

 ways placed on the upper surface, the under part 

 being perfectly devoid of them, but shining and 

 marked with nerves, corresponding to the partitions 

 at the base of the cells. 



The Polypidoms of this genus have tubular cells, 

 projecting in the upper part, large and compressed 

 below: the opening is large, and usually irregular, 

 with the border turned in, perhaps resulting from 

 desiccation. Those at the extremity of the branches 

 are nearly straight ; the others become less so in pro- 

 portion as they approach the base. 



