560 SYDNEY J. HICKSON. 



skeleton of Tubipora are the tabulae. These may consist either 

 of simple flat partitions in the cavity of the corallite (fij^, 6), or 

 they may be concave or convex, or cup-shaped (fig. 6) ; they 

 may be in the form of long drawn out funnels, or in the form 

 of axial tubules within the corallites (fig. 3), or assume much 

 more complicated shapes and forms. They were first referred 

 to by Pallas (21), and subsequently figured by Ellis (6) and 

 Lamouroux (13). These authors called them the "siphunculi," 

 and seem to have considered that their normal if not their only 

 condition was that of hollow tubes open at both ends. Curiously 

 Professor Nicholson has only recently fallen into the same error, 

 for he says (20, p. 221) : " The axial tube itself, so far as I 

 have seen, is always open along its entire length. . . ." 

 As, however, every intermediate condition can be found 

 between axial tubes open at both ends and simple flat parti- 

 tions exactly similar to the tabulae of the Favositidse, I shall 

 call them throughout the " tabulse.^^ 



The simple flat tabula is a condition which is very frequently 

 met with, but very often the tabula is not complete, but 

 stretches only part of the way across the cavity of the corallite. 



Sometimes only a small strand could be found, reminding 

 one of the " tongue-shaped " tabulae of the Favositidae (Nichol- 

 son, 19, p. 41), and in a few instances the tabulse were still 

 further reduced to mere spiniform projections of the walls of the 

 corallite, reminding one of the condition found in Pachypora. 



Complete tabulae were also found slightly convex or concave, 

 as in Michelinia and other Favositidae; others were cup-shaped 

 (fig. 6), and others were funnel-shaped "with the narrow end 

 drawn out to a fine point. 



A very common condition, however, is that in which the 

 tabula takes the form of an axial or inner tube, bulging at the 

 nodes and giving ofi" a varying number of short tubules to the 

 platform (fig. 3) or, as Ellis (6) puts it, ** siphunculis continuis 

 geniculatis, ad genicula radiatis." 



Frequently, however, the condition is much more compli- 

 cated. One tabula, starting from a node, is drawn out into the 

 shape of a long funnel, and passing downwards is entirely 



