MIXUTE STRUCTURE OF STROMATOPORA AND ITS ALLIES. 211 



pillars crossing the interlamiiiar spaces, and in some other cha- 

 racters as well. Having seen no example of this species in which 

 the surface is weathered, we are unable to say how these canals 

 appear superficially ; but in horizoutal sections they seem to be 

 generally oval or elongated canals or wall-less spaces, freely open- 

 ing into the interlaminar spaces. 



7. Tubes (j/* Caunopora. — Of a very difterent character to the 

 preceding are the vertical tubes found in the genus Caunopora. 

 The only example of this genus that we have been able to examine 

 by means of microscopic sections is Caunopora placenta, PhilL, from 

 the Devonian rocks of Devonshire. In this form the general 

 structure of the mass is very similar to that of a typical Stroma- 

 topora, such as S. striatella, D'Orb., except that the radial pillars 

 are not so well developed. There is, however, the special feature 

 that the entire mass is perforated by numerous discontinuous (?) 

 vertical tubes penetrating the horizontal laminae at right angles. 

 These tubes have strong calcareous walls, are about | line in dia- 

 meter, have no vertical septa, but sometimes exhibit transverse 

 calcareous plates, which look like continuations through them of 

 the horizontal laminae. The tubes are also sometimes connected 

 by transverse tubular canals of considerable size. From the 

 general form of these tubes, from their strong calcareous walls, 

 and from the occasional presence of lateral connecting-tubes, we 

 w^ere led to think it possible that Caunopora might have been 

 founded upon species of Stromatopora which had grown round and 

 gradually enveloped a colony of Syringopora. Some silicified spe- 

 cimens of a Caunopora from the Devonian of Canada certainly 

 look very like this. The tubes of Caunopora, however, are hollow, 

 or at most have a few simple transverse tabulae ; and we have 

 seen no traces in them, either in vertical or horizontal sections, of 

 the infundihuliform tahulce so characteristic of the Syringoporce. 

 We have also many silicified specimens of Caunopora {Stromato- 

 pora) perforata, Nich., in which the surface, with the openings of 

 these tubes, is well seen. In this species, the entire fossil forms 

 a thin and extended expansion, and the mouths of the tubes are 

 all slightly elevated above the surface. Had the fossil grown 

 round a pre-existent Syringopora, it is hardly possible for it to 

 have presented these characters. 



For the above reasons we are inclined at present to reject the 

 view originally put forth by Ferd. Hoemer, and subsequently 

 adopted by Yon Eosen, that Caunopora is founded upon Stroma- 



