MIDDLE DEVONIAN AND CAKBONTFEBOUS CORALS — ETHERIDGB. 261 



One remarkable peculiarity was noticed in this coral, a tendency 

 to form spots or areas of small dimensions, from three to four 

 millimetres in diameter, in which the corallites are more than 

 ordinarily irregular, but around which the others do not show 

 any tendency to revolve. 



The walls of the corallites are somewhat thickened, but I have 

 not succeeded in detecting any definite trace of a primordial wall. 



In a transverse section the fission of the walls is at times very 

 apparent, and is indicated by a projecting inwards of the newly 

 formed wall into the visceral chamber of an old corallite. 



In a longitudinal section the oblong visceral chambers are filled 

 with clear calcite, with here and there chalcedonic blebs along 

 the walls. The eye is also struck with the variable diameter of 

 the tubes, arising from causes already explained. 



The mural pores are large and very irregularly distributed, and 

 have a longest diameter of one third of a millimetre. The pores 

 appear as oval openings whenever the plane of the section is 

 coincident with that of one or more of the walls, or as gaps in 

 the latter indicated by a break in their continuity. 



The tabulae are, as a rule, distant and variable in direction, 

 being eiiher horizontal, concave, or less frequently oblique. They 

 may be on the same level in contiguous tubes, or strictly alternate, 

 but no satisfactory evidence exists of a tendency on the part of 

 any of them to become vesicular, as in D. alveolaris, Nich., " when 

 the section happens to intersect one of the rows of confluent 

 corallites in any direction except a directly transverse one." 



I have quite failed to detect any trace of septa, nor have I 

 seen anything at all analagous to the peculiar moniliform structure 

 depicted in one of Nicholson's sections. I would suggest the 

 possibility, nothing more, of these circular or oval bodies being 

 blebs of chalcedony. A similar appearance is at times seen in 

 some of our Palaeozoic corals. 



Desmidojyora was proposed by Nicholson for a Wenlock Lime- 

 stone coral, nearly related to Alveolites, but difiering from the 

 latter and other known genera of Favositidse as follows : — (1.) 

 The primordial wall is entirely wanting. (2.) Some of the coral- 

 lites are united in sinuous serial rows by a deficiency of their 

 walls on corresponding sides, the calices becoming winding laby- 

 rinthine grooves. (3.) Absence of septa, or septal spines. (4.) 

 In the circumscribed corallites the tabulae are simple, but in the 

 serially united corallites they become vesicular. (5.) Increase by 

 fission. 



The Australian coral, I now refer to this genus, agrees with 

 all the above characters, except that the evidence of vesicular 

 tabulae is not clear. 



Named in honour of the lafce Prof. H. A. Nicholson, m.d., &c. 



Log. — Cave Flat, Murrumbidgee River (Aust. Mus.) 



ffor. — The Cave Limestone — Middle Devonian. 



