FLUSTRA. 353 
Flustra may be seen every day on our shores, and yet many, 
year after year, have paced the shore without ever observing 
them, or only regarding them as so much grey crust, quite 
undeserving of their attention. 
9. Frustra cortacea, FL. Forbes. 
Hab. On old shells. Isle of Man, Prof. Forbes; Fowey 
Harbour and Peterhead, not uncommon, Mr. Peach; on 
old shells, dredged off Sana Island, Mr. Hyndman. 
The cells broadly elliptical, having generally two hollow 
tubercles on the posterior angles of the aperture. 
10. Fuusrra? tingata, Professor Jameson. 
Hab. On rocks, shells, seaweeds ; common. 
This species spreads like a Lepralia, in round, and often 
in irregularly-shaped, patches. The cells are oval or ob- 
long, sometimes with short stout spines, that meet across 
the cell very like Lepratia nitida, except that they are never 
joined. At other times the spines are long and shaggy, 
covering the cell; but instead of uniting, inclining towards 
the mouth, as we may call it, of the cell, where, in the 
outermost cells, the spines are so long as to form a kind of 
bushy beard. Several distinguished naturalists are disposed 
to think that this is not a distinct species, but a peculiar 
state of L. nitida or L. ciliata. I remember suggesting 
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