566 PROF. E. J. GAEWOOD OX THE LOWER CARBONIFEROUS [DoC. I912, 



dicularly to the walls of the tubes (fig. 4). Yerfcical sections cut at 

 right-angles to a corallite-wall show two perforations below the 

 base of the wall and on each side of it, representing transverse 

 sections of the two ring-canals of contiguous corallites (fig. 4, p. 565). 

 From these, in many sections, tubes can be observed passing 

 obliquely outwards and upwards, and penetrating the floors of the 

 calices at the base of the walls, where they terminate at the surface 

 to form the pores already described. In horizontal sections, pre- 

 pared so as to expose the base of the walls a short distance below 

 the floors of the calices, the system of ring-canals and their con- 

 necting tubes can be Avell seen, the canals being rendered conspicuous 

 by their infilling of darker argillaceous material (fig. 6). 



Affinities and differences.- — In general appearance in 

 hand-specimens this organism, especially when weathered, closely 

 resembles the form from the Avon section referred by Dr. Vaughan 

 to Cleutopora (Michelinia) geometnca Ed. & H.^ It difffers, how- 

 ever, from this genus, as described and figured by Nicholson 

 {op. supra cit.), in the following points : — 



1. The absence of the trabecular structure which characterizes that genus. 



2. The presence of compact fibrous coenenehyma, forming the whole of the 



corallum. 



3. The presence of a definite system of ring-canals and branches. 



4. The presence of a well-developed basal epitheca, which is unattached. 



From Pleurodictifum the form here described differs by the calices 

 being low and vertical, not funnel-shaped ; by having no trace of 

 tabulae or septal spines ; by not being attached; and by the absence 

 of the commensal vermiform body. Again, the ring- canals which 

 are so characteristic of Vauglicmia have never been observed in 

 Pleiirodictyum. The former resembles Pleurodictyum in the presence 

 of intra-mural pores and of a concentrically striated basal epitheca. 

 It differs from Pcdcmcis~ in 



1. Having a much greater number of calices. 



2. The corallites not being wedge-shaped, but arranged with their walls 



perpendicular to the basal plate. 



3. The calices having narrow and polygonal walls rising from the basal 



plate, and not excavated as circular pits in the general mass of the 

 corallum. 



4. The absence of vertical striae in the calices. 



5. The regular arrangement of the perforations to form ring-canals. 



6. Not being attached. 



It resembles Palceacis in having rows of pores connecting the 

 corallites, but the minute structure of the basal plate of Palceacis is 

 unknown. 



It resembles more closely in its internal structure Microcyatlius,^ 

 which is formed of fibrous calcareous tissue, and in the possession 

 of a wrinkled basal epitheca ; also in the possession of a porous 

 coenenehyma, which characterizes the base and spaces between the 



1 Proc. Bristol Nat. Soc. n. s. vol. x (1903) p. 99. 



'' J. Haime, in H. Milne Edwards, ' Hist. Nat. Corall.' vol. iii (1860) p. 171. 



3 G. J. Hinde, Q.J. G. S. vol. Iii (1896) p. 447. 



