THE STRUCTURE AND RELATIONS OF TUBIPORA. 561 



enclosed by a similar tabula proceeding from the next lowest 

 node, and the two pass some distance down the corallite as a 

 tube within a tube (fig. 4). This condition, which was first 

 discovered by Professor Moseley, (18) is of fjreat importance in 

 the consideration of the relations between Tubipora and Syrin- 

 gopora. In one instance, I have observed the two tabulae, after 

 passing some distance down the corallite apart from one another, 

 fuse together to form one tube, as they do in Syringolites. 



Another example' I have met with is of some interest, from 

 its giving a superficial resemblance to certain Zoantharian 

 corals. A tabula, in the form of an axial tube, completely 

 closed above by a convex tabula, gives off eight delicate tubuli 

 to the platform at the node. When viewed from above, this 

 has exactly the appearance of a central solid columella con- 

 nected to the wall of the corallite by eight septa. (See wood- 



FiG, 1. — Diagram of septiform tubulae of Tubipora. (a), axial tabula from 

 which eight processes radiate. 



cut, fig. 1.) When we remember that in many instances the 

 presence of septa-like structures is the only reason for placing 

 certain fossil forms amongst the Zoantharia, examples such as 

 the one just mentioned showing structures which might have 

 been mistaken for septa and columella, had Tubipora been 

 known only in a fossil condition, become of importance. 



It would be, however, an endless task were I to attempt to 

 describe the varieties of tabulse met with in Tubipora, and I 

 think it is only necessary for me further to mention that the 

 conditions met are often of the greatest })ossible complication. 

 In fig. 5 is represented a condition illustrating this statement ; 



' This example, and many others illustrating the varieties of the tabulse of 

 Tubipora, may be seen in the Oxford University Museum. 



