20 INTRODUCTION. 



instead of the Bath Oolite Limestone ; Diastopora at once disap- 

 peared, and Berenicea became very abundant. The British Museum 

 Collection includes 47 specimens of Berenicea from the Bradford 

 Clay, and only 7 specimens from the Great Oolite. All Diastopora 

 begin in a Berenicea stage (Fig. 7) ; and it is not at all improbable 



FIG. 7. The initial Stomatoporoid cell of a Diastopora, and expansion to 

 Berenecoid condition. Diastopora davidsoni, Haime. Bathonian: 

 Kanvillo. 60381. 



that, owing to the changed conditions, the young of the erect forms 

 continued to grow in the encrusting form. Thus, perhaps in a 

 single generation, all the Diastopora changed to Berenicea. When 

 later on the deposition of clay ceased, and the limestones of the 

 Forest Marble were laid down in the same locality, the conditions 

 then were generally unfavourable to Bryozoa, so that specimens 

 of the class are rare. But those which are found are Diastopora, 

 and not Berenicea', so that the encrusting forms may have given 

 birth to a frondose generation. 



It may be suggested that such a sudden change of habit is 

 improbable, and that it is more likely that the Diastopora were 

 killed when the muddy conditions came, and that the Berenicea 

 came from some adjoining area and replaced them. But this does 

 not appear to be the true explanation; we do not know of any 

 area in which Berenicea were abundant at the time, while there 

 is a certain parallelism between the variation of Diastopora and 

 Berenicea. Thus, Diastopora foliacea, Lamx,, resembles Berenicea 

 compressa (Gold.), for both have long tubular zocecia and distant 

 apertures. Similarly Diastopora davidsoni, Haime, may be the 

 erect form of Berenicea scolinula (Mich.), for both have fairly long 



