BEYOZOA OE POLYZOA. 



119 



Examples : Flusira (Fig. 61), Memhranipora (Fig. 65 a), Ony- Gallery 

 clwcella (Fig. 65 I). VIII. 



In many Bryozoa certain individuals are modified for 

 special duties. Tiius in the Cheilostomes the growth of the 

 operculum has produced snapping beaks, called avicularia, 

 and long movable bristles, called vibracula; the positions 

 occupied by these appendages can be detected in the fossils 

 (Fig. 65). Sometimes individuals are set apart and modified 

 for reproduction, sometimes special pouches for the reception 

 of the developing eggs are attached to the chambers (Fig. 65 a). 



Fig. 64. — Cyclostomatous Bryozoa from the Bathonian (Bradford Clay) of 

 England, a, Stomatopora dicJwtoma, part of an encrusting colony, 

 natural size, and magnified 25 diameters, b, Be7'enicea compressa, an 

 encrusting colony, natural size, and part of it magnifi.ed 12 diameters. 

 (After J. W. Gregory.) 



These modifications suggest explanations for the smaller 

 chambers and tubes interspersed among the normal ones in 

 the fossils of extinct Orders. 



We may now briefly review the exhibited specimens. 

 The British series begins with some from the Ordovician Case A5, 

 rocks of Wales. These are so poorly preserved that they ^^^^ 

 can only be determined by the help of better specimens from 

 American rocks of the same age. Most of them are Trepo- 

 stomes or Cryptostomes. 



The Silurian Bryozoa are in a better state, and the Case A5, 

 specimens from the Wenlock Limestone include some "^©^t Side. 



