CHAP. IV. ] ST. THOMAS TO BERMUDAS. 251 
conical projection, and at its summit a very small, oval, smooth 
space, the indication of a point of attachment. Twelve radi- 
ating ridges proceed from the base of the central projection, 
one to each of the tubercles, becoming more marked as they 
proceed outward. The ridges are beset with small pointed 
tubercles, which, with the ridges themselves, increase in size 
from the centre outward. These small tubercles are arranged 
to some extent at regular intervals along the ridges, and there 
are traces of a series of concentric wavy lines, corresponding in 
position to the several rings of tubercles. These are evident- 
ly lines of growth, showing the outline of the corallum at suc- 
cessive steps, the tubercles corresponding to these lines having 
been originally marginal, but having become nearly obliterated 
by fusion with other tubercles successively formed outside them, 
and sometimes entirely lost in the resulting ridge. In one spec- 
imen a second series of very delicate ridges are clearly marked, 
radiating outward for a short distance from the base of the 
central cone, and corresponding with the secondary and tertiary 
costee. The whole surface of the base of the corallum is cov- 
ered with small, rounded, closely apposed granules. The large 
marginal tubercles of the base are from 4 to 5 mm. long, and 
about 4 mm. broad at their origin. Superiorly they are joined 
by slightly elevated, rounded ridges, the continuations into them 
of the primary and secondary costw. The majority of the tu- 
bercles taper outward, but some are obtuse. They terminate 
in three or four irregularly disposed spines. Two, or even 
three marginal tubercles are sometimes fused together laterally 
into one mass. 
From the region of origin of the marginal tubercles of the 
base, the wall of the calicle slopes upward and outward at an 
angle of 60° with the plane of the base, its height above the 
base being about 14 mm. The rounded ridges described as 
passing into the turbercles reach upward to the margin of the 
calicle, and the external edges of the exsert primary and second- 
