2 70 TABULATE CORALS. 



commonly exhibiting at regular intervals definite areas occu- 

 pied by corallites which are larger or smaller than the average. 

 These areas are commonly elevated above the general surface, 

 and are then known as " monticules," 



Obs. — The corals which are usually known by the name of 

 Montinilipora, together with the forms allied to this, constitute 

 perhaps the most intricate and difficult assemblage of Palaeozoic 

 fossils with which the zoophytologist is called upon to deal. I 

 had originally intended to devote considerable space to this 

 group ; but I find that the limits of this work will not allow of 

 my carrying out this intention, and I have decided rather to 

 publish an entirely separate memoir upon the MoiiticidiporidcE. 

 Here, therefore, I shall merely give a brief outline of the 

 general results of the investigations which I have been carrying 

 out as to the internal structure of the corals usually referred to 

 Monticiilipoi^a and allied types. 



[It may not be out of place if I add a iQ\v remarks here as to the proper 

 method of making thin sections of the MonticidiporidcB ; for the results which I 

 have obtained will certainly not be reached by other investigators, unless they 

 follow the plan of procedure which I have 'adopted. In any massive or ramose 

 Monticidipora (and, I may add, in any coral similarly composed of tubular 

 corallites radiating from an imaginary axis), the true structure can only be under- 

 stood by making three distinct sections. Two of these sections are perfectly 

 obvious and natural ones — one being transvejse, or at right angles to the long- 

 axis of the corallum, while the other is vertical, and is taken iti the median plane 

 of the corallum and parallel ivith its long axis. I used myself to consider these 

 two sections sufficient, and probably others have entertained a similar opinion. 

 Owing, however, to the fact that the diverging corallites often very materially 

 alter their character just before they open on the surface, and owing also to the 

 generally very limited inward extension of the interstitial small corallites (the 

 so-called " coenenchymal tubules"), as also of the curious intertubular spines 

 which are commonly present, it is absolutely necessary to make a third series 

 of sections which should run Just below the calices of the corallites and at right 

 angles to the long axis of the latter. The direction in which it will be necessary 

 to cut any given coral to obtain sections of this nature will always vary with 

 the form of the corallum ; but these sections may be termed tangential, as they 

 must in all cases be taken in a direction tangential to the calicular surface and 

 just below that surface. Sections of this kind are most instructive and im- 

 portant ; and from my ignorance of their value and consequent neglect to pre- 

 pare them, I have fallen into grave errors, or failed to seize the true structure, 

 in the case of certain forms of this group, of which I have on former occasions 

 described the minute characters.] 



