THE NATURE OF CAUNOPORA. 125 



stones of Devonshire, in which " Cannoporce " are extremely abundant, while 

 Syringoporce are nearly unknown. Of course, in such cases it might be said that 

 the reason of the absence or scarcity of Syringoporce is merely that these Corals 

 have wholly or mostly become commensals with Stromatoporoids, and have thus 

 become " Caunoporce ;" but till it is proved that the " Caunopora-tnbes " belong to 

 Syringopora, this seems to me to be to some extent begging the question at issue. 

 It seems, at any rate, certain that if we accept Syringopora as the Coral which 

 is concerned in the production of " Caunoporce" and " Diaporce " we must at the 

 same time make two admissions which are attended with more or less of doubt and 

 difficulty. In the first place, we must admit that the Syringoporce, when growing 

 commensally with Stromatoporoids, to some extent alter their normal mode of 

 growth, in so far as to grow with much greater regularity and uniformity than 

 they do in their free state. This admission is not of much importance, because 

 we must make the same, on a considerably larger scale, if we suppose Aulopora to 

 be the Coral concerned in the production of " Caunoporce" and "Diaporce." A 

 much more important admission is that we are compelled to suppose that many of 

 the Syringoporce which give rise to " Caunoporce " belong to species which are 

 unknown in their free state, and which never occur except when thus living com- 

 mensally with some Stromatoporoid ; since no known species of this genus of 

 Corals has tubes nearly so minute as those of certain " Caunoporce." The diffi- 

 culties connected with this admission are so great that at present I do not see how 

 it is possible to accept Syringopora as being the genus of Corals usually concerned 

 in the production of " Caunopora "-colonies. 



(d) Aulopora as the Commensal of Caunopora. — As previously stated, Roemer 

 ultimately came to the conclusion that Aulopora, and not Syringopora, was the 

 Coral concerned in the production of " Caunoporce." If we take the thin laminar 

 expansions of the " Diaporce" and of some " Caunoporce" then there is no doubt 

 that the embedded tubes, if divested of the enveloping Stromatoporoid, would 

 much more nearly resemble an Aulopora-colonj than a Syringopora. In some very 

 thin specimens, the embedded tubes consist of nothing except an irregular series 

 of horizontal stolons, sending out short erect branches, which do not seem to be 

 connected by cross-tubes. In most specimens, however, the tubes grow vertically 

 upwards to the full thickness of the coenosteum, and are connected by cross-tubes 

 at varying heights, thus losing their general resemblance to Auloporce. Even in 

 the thicker examples of the laminar " Caunoporce " and " Diaporce" it is, however, 

 not unusual to find that horizontal stolons are developed at more than one level 

 in the fossil, showing that different sets of the " C aunopor a-tubos " succeeded each 

 other vertically at intervals of time. As a general rule, however, the tubes are 

 continuous in the particular types here alluded to. 



The tabuke of the " Caunopora-tubes" though more like those of Syringopora 



17 



