118 GUIDE TO THE FOSSIL INVEETEBEATE ANIMALS. 



G-allery and Fencstella (Fig. 63). The Cyclostomata were dominant 

 during the Mesozoic Epoch ; their chambers have simple 

 round openings at their ends, with no covering. Examples : 



Fig. 62. — A Trepostomatous Bryozoan, Callopora subnodosa, Ordovician 

 (Cincinnati group), N. America, a, fragment of a colony, natural 

 size, b, part of the surface, magnified 12 diameters, c, part of a 

 vertical section, showing tubes of differing size crossed by diaphragms, 

 magnified 18 diameters. (After E. 0. Ulrich.) 



Fig. 63. — A Gryptostomatous Bryozoan, Fenestella vera, Devonian (Hamilton 

 group), N. America, a, fragment of a colony, obverse, showing the 

 fenestrae, to which the genus owes its name, as white spaces, and the 

 chamber-openings as small dark holes, b, reverse of same, showing 

 fenestrae only, c, section of same, passing from near obverse surface 

 on left to near reverse surface on right, a and b magnified 9 diameters ; 

 c, 18 diameters. (After E. 0. Ulrich.) 



Stomatopora, Berenicea (Fig. 64). In the Cheilostomata^ 

 which reached their present dominant position in Cainozoic 

 time, the opening is removed from the end of the chamber, 

 is constricted, and provided with a movable lid (operculum). 



