GENERA OF FAVOSITID^. 151 



absence in parts of the corallum, together with the fact that 

 they traverse the walls in different directions, would entirely 

 negative this view. 



The only remaining points in the anatomy of Pleurodictyum 

 stylopJiorum which need notice, concern the condition of the 

 septa and tabulae. Returning again to transverse or tangential 

 sections of this species (PL VIII., fig. i a), we find the septa 

 represented by short spines arranged in vertical rows, quite 

 resembling the same structures in various species of Favositcs. 

 The tabulae are seen in long sections (PI. VIII., figs, i and i b) 

 to be always well developed, and to have the form of strong 

 horizontal flexuous plates, which are not strongly convex, and 

 which do not give rise to anything that could be appropriately 

 called " vesicular tissue," though they not uncommonly unite 

 with one another to a limited extent. Owing to the shortness 

 of the corallites, there are usually not more than four or five 

 tabulae in a single tube. 



Upon the whole, it will be seen by the preceding description 

 that there is a close relationship between Pleurodictyum, Goldf , 

 and Michelinia, De Kon., and it is a matter of question if the 

 two genera can be kept apart. Should it be found necessary to 

 merge these two genera, it is Michelinia which will have to 

 give way to the older Pleurodictyum, and not, as some writers 

 assume, the latter to the former. In the meanwhile, however, 

 I think it safest to keep the two distinct until, at any rate, the 

 structure of Pletirodictyuvi has been fully worked out. If this 

 course be followed, Pleurodictyum, Goldf., will contain corals 

 in most respects quite similar to Michelinia, De Kon., but dis- 

 tinguished by their small size and discoid form, and by the fact 

 that the tabulae are not markedly convex, and do not subdivide 

 or inosculate to any notable degree. It is possible (though not 

 likely) that the " intramural canals " which I have described 

 as occurrino- in Pleti-rodictyum may be found to distinguish the 

 o-enus further from Michelinia. I need only add that it is 

 certain that Dr Ferd. Roemer must have been misled by 

 appearances when he asserts (Leth. Pal., Explanation of PI. 



