2 76 TABULATE CORALS. 



as well. At any rate, I feel sure that the difficulty of deter- 

 mining this point in the case of the smaller species is so great 

 that I am right in the formerly expressed opinion that this 

 character alone should not be accepted as an adequate generic 

 distinction between ChcBtctes and Montiadipora (Quart. Journ. 

 Geol. Soc, vol. XXX. p. 500). 



There is at present no evidence as to the existence of 

 " mural pores " in Moiiticulipora or its allies. Considering the 

 minute size of the tubes, and the great difficulties which com- 

 monly attend the detection of these apertures in microscopic 

 sections, the non-recognition of pores does not absolutely imply 

 their non-existence. We know that pores are present in the 

 similar-looking Sienopora, Lonsd.; I have previously shown that 

 similar apertures exist in the Favosites Bowerbanki, E. and H. 

 sp. of the Upper Silurian, which has hitherto been regarded as 

 a Moiiticulipora ; and, as before remarked, I have recently 

 examined a specimen from the Upper Silurian of Dudley, in 

 which the general characters of Montiadipora are present, but 

 the walls are minutely porous. Moreover, the microscopic ex- 

 amination of weathered or fractured surfaces often brings to 

 light deficiencies in the walls of the tubes, though whether these 

 are accidental, or are really of the nature of " mural pores," is a 

 point upon which I have hitherto been unable to satisfy myself 

 In the want of direct and positive evidence, we must at present 

 assume the walls in Montiadipora and its allies to be imper- 

 forate. At the same time I should not be surprised if future 

 and more extended investigations should show that mural pores 

 really exist ; though it may be safely assumed that any struc- 

 tures of this kind that may be detected will prove to be pro- 

 portionately more minute, and more irregular in their size and 

 distribution, than is the case with these openings in the typical 

 Favositidcs. 



Whatever may be the condition of the walls in Montiailipora, 

 microscopic examination brings out very clearly the important 

 fact that in the vast majority of cases, and probably invariably, 

 the corallum is truly dimorpJdc, and consists of two different 



