chief Oeneric Types of Palceozoic Corals. 



299 



Externally, the septa are united hy numerous close-set deli- 

 cate dissepiments, whicli are sometimes rectangular, sometimes 

 finely anastomosing and reticulate (PL XII. figs. 1-6). The 

 dissepiments give rise to an exterior zone of vesicular tissue 

 of an extremely dense and minute character. As seen in 

 longitudinal sections (figs. 2 A, 3 A, 6 a), the vesicles of this 

 zone are exceedingly small lenticular cells, which are arranged 

 in layers directed upwards and outwards from the central 

 tabulate area. 



As regards the relationsliips of the genus, Koninckophyllum 

 may be said to be distinguished by characters of an unusually 

 fundamental nature. In some respects it is nearly allied to 

 Diphyphyllum and to some of the forms of Cyathophyllum 

 (such as C. paracida, j\rCoy) ; but it is broadly separated 

 from these genera by the possession of a well-developed, com- 

 pact and styliform columella. From LophophyUum^ E. & H., 

 it is distinguished by the totally difterent form and connexions 

 of the columella, and the less developed condition of the septa, 

 and, even more strikingly, by its extraordinarily minute and 

 dense zone of vesicular tissue forming the ])eriphery of the 

 corallum. From Lithostrotion^ again, it is separated by the 

 much more rudimentary state of the septa, the greater deve- 

 lopment of the vesicular zone, and the fact that the corallum 

 is always compound in the former, whilst it is usually simple 

 in the latter. 



There remains, finally,only the genus Axop)hyUum, E. & H., 

 which need be considered here, though its characters are such 

 as really to render its separation trom Koninckophyllum a matter 

 of no difficulty, as will be at once seen by a reference to the 

 annexed woodcut and the subjoined description. The corallum 



Longitudinal section of AxophyUum Konincki, E. & H., the type species 

 of the jjenus A.rophylbtm. After Mihie-Echvards and Ilaime. 



20* 



