INTRODUCTION. 



11 



It is unnecessary further to refer to the soft parts of the Bryozoa, 

 but the skeleton must be considered with greater care. We may, 

 however, neglect the skeleton of the Cheilostomata, for only two 

 species belonging to this order are known in the Jurassic series. 

 Attention may therefore be confined to the elements of the shell of 

 the orders Cyclostomata and Trepostomata. 



4. THE TERMINOLOGY OF THE SHELLS OF THE CYCLO- 

 STOMATA AND TREPOSTOMATA. 



Zooecium. The tubular skeleton of the Bryozoite. Its simplest 

 form among the Cyclostomata is a simple open tube. The first 

 advance on this is for the distal end of the tube to be bent round, 

 or reflexed, as in Stomatopora (Fig. 2b). In some cases the 



0^-v 



abed 



f 



FIG. 2. Diagrams of zooecia of Bryozoa. a-c. typical Cyclostomatous zooecia; 

 a. simple form, as in Tubulipora ; b. reflexed peristome, as in Stoma- 

 topora ; c. lateral aperture, as in Haplocecia ; d. zooecion with 

 diaphragms ; e. zooecion with cystiphragms ; /. section of three 

 zooacia with mesopores ; g. section across a Cheilostomatous zooecion 

 with ooecion. 



a.= aperture; m. = mesopore; ov. = ooecia ; z. = zooecia. 



distal ends of zooscia; with such reflexed peristomes, are enlarged, 

 or continued beyond the aperture; in such cases the aperture is 

 somewhat contracted, so that it is smaller than the diameter of the 

 zocecium, and is lateral in position, as in the genus Haplocecia. 

 In such cases the zooecia closely resemble those of simple forms 

 of Cheilostomata. 



The zooscia are generally of uniform diameter ; but some are 

 larger in one part than in others, and maybe ** bulging," "fusi- 

 form," or "pyriform." The zooecia are usually open throughout, 

 but sometimes they are divided by transverse " diaphragms." 



The wall of the zooecium is calcareous, and is usually somewhat 

 porous in structure. When the pores are large the shell is said 



