240 Mr. J. Young on the Structure of 



In my former paper in the ' Annals ' I noted the occurrence 

 in the earlier stages of F. incrustans of small polygonal cells 

 that filled in the interspaces between the autopores. In this 

 earlier stage I had accepted as probably correct Mr. G. 

 R. Vine's identification of the organism with Ceramopora, 

 in which genus he had placed it, rather than with Bere- 

 nicea and Diastopora^ in which its younger forms were for- 

 merly placed. Messrs. Nicholson and Foord, however, in 

 their paper take exception to this identification with Geramo- 

 pora, and state that this genus is distinct in all its stages 

 from Fistuli'pQTa. The presence or absence of the poly- 

 gonal cells (mesopores) here noted seems to have raised 

 some doubt in the minds of these authors as to the correct 

 identification of the younger stage of F. minor, M'Coy, 

 with the organism which M'Coy figures and describes as 

 Berenicea megastovia, they stating (p. 503 of their paper) 

 that " it is not possible to be absolutely certain of this without 

 an examination of M'Coy\s original specimen, especially as 

 McCoy's figure of Berenicea megastoma does not exhibit 

 any mesopores, nor does his description of the species contain 

 any allusion to the presence of interstitiial tubes." Perhaps 

 I may be able to somewhat dispel this doubt by stating that 

 we find in our Scottish limestone-shales examples of the 

 younger stage of F. minor that agree exactly with M 'Coy's 

 figure and description of Berenicea megastoma. That is, they 

 are found as adherent " spot-like crusts " that sometimes 

 show the open mesopores on the surface ; in other examples, 

 like M' Coy's specimen, the mesopores are seen to be covered 

 by a thin calcareous layer of sclerenchyma-deposit that I shall 

 notice later on. There is thus every reason to believe that 

 M'Coy's specimen had the mesopores closed by a similar cal- 

 careous layer, and the reason why they were not noticed by 

 him is probably due to the fact that he only saw one example 

 of the organism, the one figured. My reason for this belief 

 is that the organism in the early stage seems to be rare in 

 Ireland, he giving only one locality for it and mentioning no 

 other examples. Had he seen other specimens he could 

 hardly have failed to observe the mesopores on the surface of 

 some of them. In our Scottish specimens they are seen to 

 occur on the surface of the organism in all its stages of growth, 

 but are sometimes closed or partially closed by the calcareous 

 outer layer that I noted in my former paper (p. 428), which Dr. 

 Lindstrom terms the " Thecostegites stage." I also find that 

 Mr. Ulricli has noticed this closed condition of the mesopores 

 in several genera of American Bryozoa, and terras the 

 obscuring layer a secondary deposit of sclerenchyma that 



