THE NATURE OF CAUNOPORA. 113 



any vertical sections which shall intersect any given tube along its entire length, it 

 is not possible to assert positively that the individual tubes of the " Caunoporce ' 

 are continued through the entire thickness of the larger examples without interrup- 

 tion. In laminar specimens of "Caunopora" it seems almost certain that the 

 majority of the tubes are continued straight from the base of the organism to the 

 surface, without any interruption, merely giving off horizontal connecting-processes 

 to adjoining tubes at intervals. In such specimens I have often traced a single 

 tube, without a break, through a vertical thickness of an inch or more. In the 

 more massive specimens, which often reach several inches in thickness, I have little 

 doubt that the tubes also run for very long distances without interruption, though 

 I am not able to say that they are continued from the base to the surface. [I have 

 traced a single tube for over two inches.] In such specimens, therefore, the 

 " Caunopora-tubes," if divested of the surrounding tissue, would more nearly 

 resemble a colony ot Syringopora than one of Aulopora. They would, however, 

 differ from any ordinary Syringopora in the regularity with which they are spaced, 

 and, still more, in their often very minute size. 



In other specimens, again, parts of the organism may be charged with " Cauno- 

 pora-tubes," while they may be wanting, or very sparsely developed, in other parts 

 of the same. In other cases, again, the " Caunopora " assumes a cylindrical shape, 

 and then the tubes radiate outwards in all directions to open on the surface of the 

 specimen. A modification of this is seen in some specimens where the organism 

 consists of a series of parallel cylinders united by a larger or smaller amount of 

 interstitial tissue. In such cases, each cylinder is generally traversed by its own 

 set of " Caunopora-tubes,'' radiating outwards from its central line. 



Another important consideration in the case of the " Caunoporce " and " Dia- 

 poros " is that of the nature of the Stromatoporoid in which the " Caunopora-tubes " 

 are enveloped. I have examined many hundreds of these fossils, but it has not 

 been in more than perhaps a dozen instances that I have met with anything that could 

 be properly called a " Caunopora " or " Diapora" unless the enveloping Stromato- 

 poroid has belonged to the " Milleporoid " section of the Stromatoporoids, i. e. 

 to that section in which the skeleton is of the more or less completely reticulated 

 type. In fact, almost all the " Caunoporce" and "Diapora}" belong, as regards 

 the tissue of the enveloping Stromatoporoid, to the genera Stromatopora, Goldf., and 

 Stromatoporella, Nich., and it was upon the difference in the structure of the 

 skeleton in these two genera that Bargatzky founded his genus Diapora, as distinct 

 from Caunopora, Phill. Until recently, I should have said that all specimens of 

 " Caunopora " and " Diapora " belonged, as regards the enveloping Stromatoporoid, 

 to the genera Stromatopora and Stromatoporella. Dr. Hinde has, however, shown 

 me a specimen of a " Caunopora " from the Corniferous Limestone of Canada, in 

 which the enveloping Stromatoporoid is referable to the genus Clathrodictyon. 



