26 BRITISH STROMATOPOROIDS. 



(2) The tubes of Diapora laminata are much smaller in their diameter than 

 are the tubes of Aulopora repens, the common Devonian species of Aulopora. 



(3) It is very unlikely that any organism should be able to stretch its power of 

 accommodating itself to changes of environment to the extent demanded by 

 Roemer's theory of the commensalism of Caunopora. It is known from various 

 observations, including those of Roemer himself (' Leth. Pal.,' p. 519), that each 

 corallite of Aulopora ceases to grow so soon as it has begun to throw out buds, 

 remaining thereafter completely stationary, and no longer extending itself verti- 

 cally. In the case of Caunopora, if we admit the correctness of Roemer's views, 

 we should have to suppose that, long after the corallites of Aulopora have thrown 

 out buds and had therefore become stationary, they are capable of beginning an 

 entirely new process of growth, as a consequence of entirely changed conditions 

 of life. It would be difficult, however, to point to an analogy to this among 

 recent organisms. So far as we can judge from what we observe at present, 

 the power of accommodation to changes of environment is only possessed by 

 organisms, to any marked extent at any rate, while they are in a state of active 

 growth. On the other hand, when the organism has reached its full limits of 

 growth and has become stationary, its power of accommodation is greatly 

 restricted, and it rapidly perishes if subjected to conditions unsuitable for its life. 



Still more recently, Prof. J. W. Spencer has described some Stromatoporoids 

 from the Niagara formation of North America (' Bulletin of the Museum of the 

 University of the State of Missouri,' vol. i, No. 1, pp. 43 — 52, 1884). The following 

 are described as new species, Caunopora Walkeri, C. mirabilis, Ccenostroma risti- 

 gouchense, C. botryoideun, and Dictyostroma reticulatum. 



Lastly, some Stromatoporoids have been described by Dr. Friedrich Maurer in 

 an extensive and valuable memoir on the fossils of the Devonian rocks of the 

 neighbourhood of Giessen (" Die Fauna der Kalke von Waldgirmes bei Giessen," 

 ' Abhandl. der Grossh. Hess, geolog. Landesanstalt zu Darmstadt,' 1885). Dr. 

 Maurer has had the great kindness to send me specimens of most of the forms 

 which he has described, of which I have prepared thin sections ; but all the 

 specimens are in an unsatisfactory state of preservation, some being dolomitised, 

 while others are highly crystallised or distorted by pressure. The form which 

 Maurer has described and figured as Stromatopora concentrica, Goldf., is (like the 

 form so named by most previous writers) an Actinostroma, and appears to be 

 referable to A. verrucosum, Goldf., sp. The form identified as Stromatopora 

 Beuthii, Barg., is the S. {Caunopora) Bupschii, Barg., in its normal condition, i.e. 

 ivithout any " Caunopora-tubes." On the other hand, S. indubia, Maur., is the 

 8. (Caunopora) Hiipschiiy Barg., with numerous " Caunopora-tubes," and greatly 

 distorted and altered by intense pressure. The species described by Maurer under 

 the name of S. turgicolumnata is identical with the form which I understand (from 



