214 A. E. Verrill—The Bermuda Islands; Coral Reefs. 
The disk and tentacles are usually dark yellowish or greenish 
brown. In contraction the membrane of the disk becomes rough or 
wrinkled in radial lines, as in the other species of the genus. 
When fully expanded the polyps rise a little above the crests of 
the collines and the disks expand to the width of the upper part of 
the calicinal valleys ; the adjacent column walls then become nearly 
vertical, leaving only narrow grooves between them, over the crests 
of the collines. The tentacles form two cycles, the inner ones a 
72 72a 
Figure 72.—Mcandra cerebrum, var. sinuosa. Brain Corai. Portion of a young 
colony, about natural size. 
Figure 72a.--The same. Portion near the margin of the same specimen, enlarged 
about 13. Both phot. by A. H. Verrill. 
little larger; they are small, rather short, obtuse or slightly knobbed 
and whitish at the tip. In contraction the disk sinks to the bottom 
of the valleys and the column walls cover the septa, becoming 
uneven over their teeth. The tentacles can be introverted in full 
contraction. 
It is much less common than the last and is rarely found except 
on or near the outer reefs. It seldom grows close to the surface, 
but is more frequent in 6 to 20 feet of water. 
It is a common West Indian and Florida coral, and often grows to 
great size there. 
