1 6 INTRODUCTION. 



as a Stomatopora, then becomes a Proboscina, and ends as a 

 Berenicea. 



It is therefore urged that the four genera in question must be 

 united into one, as it is absurd to treat as genera what are only 

 individual variations in growth. The authors, however, who accept 

 this argument in theory, only apply it partially in practice, and do 

 not carry it to its logical conclusion. In spite of such specimens 

 as that described by Pergens, Hincks keeps Stomatopora and 

 Berenicea apart; though with the fossils it is much easier to 



FIG. 4. Base of Diastopora, showing basal Berenecoid encrustation and erect 

 frond. Diastopora davidsoni, Haime. Bathonian: Ranville. 60381. 



separate Berenicea from Diastopora, than from Stomatopora. 

 Pergens, moreover, accepts the evidence of one half of his 

 specimen, and merges Stomatopora and Proboscina, but he does 

 not accept that of the other half, and keeps Proboscina and 

 Berenicea distinct. 



If the question of merging genera ended here, it would be less 

 important than it is. In typical Diastopora the zoarium consists 

 of two layers of zooecia, one on each side of the zoarial lamina; 

 the two surfaces of the zoarium are parallel, and the frond is 

 therefore thin. But in some species the fronds are narrow flat 

 ribbons, as in Diastopora calloviensis, D'Orb. ; in others, such as 

 D. lamellosa var. cervicornis, the zooecia are crowded and the fronds 

 thickened, until they are biconvex in section (Fig. 5). In many 

 zoaria of the variety mentioned, branches may be found which are 

 circular in section, and in which the zooecia are grouped into bundles 

 instead of into sheets (Fig. 6). Such branches are indistinguishable 

 from those of some species of the genus Entalophora. If, therefore, 

 the Stomatopora-ProboscinaBerenicea-Diastopora series is to be 

 included in one genus, Entalophora must also be included with 



