INTRODUCTION-. 15 



one species, specimens which D'Orbigny divided among five genera, 

 and thought he ought also to have added specimens from two more 

 genera. 



These examples show how wide are the differences of opinion 

 between those who, like D'Orbigny, attribute generic value to 

 trivial differences, and those who, like Hincks and most British 

 students of recent Bryozoa, prefer to limit the number of genera. 

 Others, again, like Haime, try to avoid the reckless multiplication 

 of names, but find it impossible to apply to the rich fossil faunas 

 the elastic definitions possible when dealing with the few living 

 representatives of the Cyclostomata. 



To understand the meaning of these differences, let us consider 

 the case of the Berenicea series more closely. Haime divided the 

 series into four genera : Stomatopora, including those in which 

 the zooecia are encrusting, and occur in single lines ; Proboscina, 

 those which are encrusting, but in which the zooecia are grouped 

 into multiple ribbon- shaped bands ; Berenicea, which again are 

 encrusting, but which spread out into sheets ; and Diastopora, in 

 which the sheets rise as erect fronds. 



This arrangement is objected to by those who prefer to restrict 

 the number of genera, on the ground that these divisions are not 

 persistent. Thus, in the case of Stomatopora and Proboscina, they 

 point out that specimens may be found in which the zoarium 

 begins as a single series and ends as a multiple series. Again, 

 they would urge that no sharp line of distinction can be drawn 

 between ribbon-shaped bands which expand slightly in the 

 middle, and encrusting sheets; and thus the division between 

 Proboscina and Berenicea breaks down. Similarly with Berenicea 

 and Diastopora ; both forms originate from encrusting zooecia, 

 which are identical in character : give the Bryozoon a broad, 

 smooth surface over which to grow, and it will remain as 

 an encrusting Berenicea', but if there be no room for this, then 

 the edge may grow upwards into a frond and become a Diastopora 

 (Fig. 4). 



Hincks therefore sinks Proboscina in Stomatopora, and Berenicea 

 in Diastopora. Pergens has described 1 a specimen which begins 



1 E. Pergens. Revision des Bryozoaires du Cretace figures par d'Orbigny: 

 Bull. Soc. beige Geol. t. iii. (1890) p. 327. 



