PLATE 42, 43, 44. 
Fossil coral. The original a Madrepora., Aggregate; 
the stirps scapiform, prismatic, unequal, coadunate* con- 
stituting, when the specimen is perfect -f-, a large, rounded, 
or somewhat nodular mass ; its surface covered with angular 
stars. The columns or stirps increased a little In thickness 
from the base upwards; sometimes slightly flexuose ; their 
sides longitudinally striated, unequal, and varying In num- 
ber from five to seven. The stars are crowded and concave; 
their margins prominent and acute ; their centres project- 
ing, pointed, and writhed or twisted like a rope. 
This species is not unfrequent in many parts of Derby- 
shire, where the limestone occurs, but is rarely to be met 
with entire : in general the specimens exhibit nothing more 
than detached parts of the original mass ; and these not often 
in a perfect state. The twisted, prominent centre of the 
stars, which forms the principal characteristic of the species, 
is frequently wanting : and hence this, fossil is liable to be 
confounded with several other Madrepores, which approach 
it in form and structure. 
Fig. 3. A small specimen in chert, its cavities filled 
with quartz. 
* But in most specimens separable. 
t This seldom : and hence the form of the mass very rarely evident. 
