118 GUIDE TO THE FOSSIL INVERTEBEATE ANIMALS. 
Gallery 
VIII. 
iiud Fencstrlla (Fig. (i:.)). The Cyclostomata were dominant 
during tlie iMesozoic Epoch ; their cliamhers have simple 
round openings at tlieir ends, with no covering. Examples : 
Fig. 02. — A Tropostoraafcous Brj-ozoan, Callopora subnodosa, Ordovician 
(Cincinnati group), N. America, a, fragment of a colony, natural 
size, h, part of the surface, magnified 12 diameters, c, part of a 
vortical section, showing tubes of differing size crossed by diaphragms, 
magnified 18 diameters, (After E. O. Ulrich.) 
a b c 
Pig. 03. — A Crj^ptostomatous Bryozoan, Fcmstella vera, Devonian (Hamilton 
group), N. America, a, fragment of a colony, obverse, showing the 
fenestrao, to which the genus owes its name, as white spaces, and the 
chamber-openings as small dark holes, b, reverse of same, showing 
fenestrao only, c, section of same, passing from near obverse surface 
on loft to near reverse surface on right, a and h magnified 9 diameters ; 
c, 18 diameters, (.\fter E. 0. Ulrich.) 
Stomatojjora, Bercnicca (Fig. 64). In the Cheilostomata, 
which reached tlieir pre.sent dominant position in Cainozoic 
time, the opening is removed from the end of the chamber, 
is coirstricted, and provided with a movable lid (operculum). 
