Prof. H. A. Nicholson—On the Favositide. 107 
1. Tangential Sections.—Sections taken tangentially to the surface 
of a Favositoid Coral, so as to cut the corallites at right angles to 
their length, very commonly exhibit the mural pores. In such cases 
the mural pore presents itself as a gap in the wall forming the 
circumference of a corallite (Fig. 1, 4, B, and C, p), the size of this 
gap depending upon the size of the pore. If the mural pore is not 
a complete perforation (as sometimes happens), then the gap is 
crossed by the thin primordial wall of the corallite, the delicate 
partition thus formed being uncovered on both sides by the layer of 
Fig. 1. 
B 
Fic. 1.—Thin sections of Favositoid Corals, showing the phenomena presented 
by the mural pores. -A, Tangential section of Favosites sp., from the Devonian of 
Queensland, enlarged six times. 4’, Vertical section of the same similarly enlarged ; 
in two of the tubes the section traverses the centre of the visceral chambers, but in 
one it corresponds in part with the wall of the corallite. B and B’, Tangential and 
vertical sections of Alveolites Labechei, E. & H., from the Wenlock Limestone of 
Tronbridge, enlarged ten times. [The septal thorns which characterize this species, 
as also A. Battersbyi, E. & H., are mostly omitted in the drawing.] Cand C’, Tan- 
gential and vertical sections of Pachypora sp., trom the Corniferous Limestone of the 
Falls of the Ohio, enlarged ten times. In all the figures the letter y indicates the 
mural pores. 
secondary sclerenchyma which elsewhere lines the wall. In the 
great majority of well-preserved specimens of species of Favosites, 
Pachypora, Striatopora, Michelinia, Pleurodictyum, Alveolites, etc., 
there is usually no difficulty in recognizing the presence of mural 
pores by the more or less frequent occurrence in tangential sections 
of the deficiencies in the walls of the corallites above described. In 
