40 TABULATE CORALS. 



Devonian — this curious feature seems to be one normal to the 

 species, being more or less fully developed in all perfect ex- 

 amples. In other species, however, it would appear to be only 

 an occasional phenomenon. Dr Lindstrom has recognised the 

 same peculiarity — as an occasional thing — in examples of the 

 Upper Silurian F. Forbesi, E. and H., and also in his Vermipora 

 {Fletcheria) clmisa, from the same formation (Ofversigt af K. 

 Vetensk. Akad Forhandhngar, 1865, PI. XXX.) 



Septa are so commonly obsolete in Favosites, or are so 

 rudimentary, that these structures were supposed to be gener- 

 ally altogether absent in the species of this genus. In reality, 

 however, the septa must be regarded as constituting one of the 

 most variable of the structures of a very variable group, and 

 not even specific value can be attached to their presence or 

 absence, or to the degree of their development when present. 

 In some cases there are absolutely no traces of septa, even in 

 specimens examined by means of microscopic sections. More 

 commonly the septa can be recognised as so many longitudinal 

 striae or ridges on the interior of the tube, each ridge being 

 really made up of a vertical series of tubercles. In other cases, 

 again, the septa have the form of radiating spines, which may 

 reach very nearly to the centre of the visceral chamber, though 

 usually considerably shorter than this. In no case are regular 

 lamellar septa developed. All the above conditions of the 

 septa — namely, their presence as radiating spines in superposed 

 rows, their development as tubercles arranged in ridges, or 

 their total absence — may be occasionally recognised in different 

 examples of the same species, or even in different parts of the 

 same specimen. The number of the septal ridges or spines, 

 when developed at all, is not constant, but appears to be most 

 commonly from twelve to fifteen. 



The genus Astrocerium, Hall [loc. cii.), was founded upon 

 examples of Favosites, in which spiniform septa are developed ; 

 but the variability of this character renders this division an 

 untenable one. 



The tabulae in the most typical forms of Favosites are com- 



