114 BRITISH STROMATOPOROIDS. 



Mr. Cbampemowne lias, further, shown me a specimen of Actinostroma, from the 

 Devonian Rocks of Devonshire, in which " Caunopora-tubes " are developed. 

 Lastly, I have myself recently collected a number of specimens of " Caunoporce" 

 from the Silurian Rocks of Oesel, in which the enveloping Stromatoporoid belongs 

 to a peculiar group of forms intermediate between Clathrodidyon and Bosenella. 



It should be borne in mind, however, that there occasionally occur specimens 

 which are penetrated by isolated or quite irregular tubes which have internally 

 much the same structure as " Caunopora-tubes," from which, indeed, they could 

 not be morphologically distinguished, but which should not be considered as being 

 true " Caunoporce " or " Diaporce." In such cases, the tubes are generally of large 

 size, are entirely irregular in their growth and distribution, run usually more or 

 less horizontally or obliquely, and sometimes are exposed over parts of the surface. 

 It seems safe to set down all such specimens as cases in which some Stromato- 

 poroid has more or less completely enveloped in its growth some Syringoporoid or 

 Auloporoid Coral. I do not mean by this to imply that the true " Caunoporce" 

 may not also be due to the combined growth of a Stromatoporoid with some 

 Syringoporoid or Auloporoid Coral ; only in that case, as will be shown later on, 

 it is necessary to suppose that the enveloped Coral has undergone certain striking 

 changes in its normal mode of growth, whereas in the specimens just alluded to 

 the embedded Coral exhibits nothing distinctive or peculiar. 



One other important general point about the " Caunoporce " and " Diaporce " 

 remains to be noticed, and it is of the highest significance. I have found, 

 namely, that all those Stromatoporoids, which are known to me as habitually giving 

 rise to " Caunoporce " and " Diaporce," occur both with and without the embedded 

 " Caunopora-tubes." That is to say, while, as a general rule, only certain 

 particular species of Stromatoporoids occur in the condition of "Caunoporce" 

 or " Diaporce," the same species can always be shown to exist without the embedded 

 tubes which characterise these two so-called genera. I shall deal more fully with 

 this point later on. All that it is in the meanwhile necessary to insist upon is 

 that this discovery would seem to render it certain that the " Caunopora-tubes " — 

 whatever the true nature may be — are not structures characteristic of particular 

 species of Stromatoporoids. On the contrary, they occur only in certain individuals 

 of those species in which they are found at all, and they are wanting in other 

 individuals of the same species. It follows from this, a fortiori, that the presence 

 of " Caunopora-tubes" cannot be employed as a character distinctive of certain 

 genera of the Stromatoporoids. We must therefore abandon the names Cauno- 

 pora, Phill., and Diapora, Barg., as the titles of genera. 



The main details of the history of opinion as to Caunopora, may be told in a 

 few sentences. The genus Caunopora was originally founded by Phillips (' Pal. 

 Foss. of Cornwall, &c.,' p. 18, 1841) for two different forms, viz. C. placenta } 



