256 Mr. H. J. Carter on the 



(PI. XV T . fig. 3, d d) would, of course, be influenced by the 

 thickness of the layers &c, as stated under " Lamince." 



On the other hand, the " curvilinear structure " (PI. XV. 

 figs. 4, 5), although also divisible into a horizontal (fig. 4) 

 and vertical (fig. 5) facies, is not so strongly differentiated as 

 the rectilinear one ; for the curvilinear element enters into the 

 vertical lineation sufficiently to give it a mixed character of 

 vertical and inflected lines (fig. 5), while the triangular linea- 

 tion is quite excluded from the vertical section in the recti- 

 linear structure. Still, while the curvilinear structure is alone 

 seen in the horizontal section (fig. 4) and the mixed form in 

 the vertical one (fig. 5), the difference is sufficiently marked 

 to obviate confusion ; besides, there is an indistinct horizontal 

 lineation in the vertical which is never seen in the horizontal 

 section, arising not from actual lines, but from structural 

 arrangement influenced by the laminar growth. 



In the horizontal section the curvilinear structure is repre- 

 sented by a vermicular fibre or thread (PI. XV. fig. 4,aaaa), 

 which, branching and anastomosing repeatedly, is not con- 

 fined to the surface as the triangular lineation in the recti- 

 linear form, but, descending perpendicularly (fig. 5, ccc), 

 gives rise to the straighter curvilinear structure observed in 

 the vertical section (fig. 5,aaaa) ; so that, in short, the curvi- 

 linear thread is horizontal in the horizontal and somewhat 

 verticalized in the vertical section of the layer, which, being 

 repeated concentrically, leads at last to the production of the 

 general mass of this kind of Stromatopora, as the rectilinear 

 does to its corallum. 



Here the intervening cavities (PI. XV. figs. 4 and 5, bb,bb, 

 respectively, now filled with transparent calcite), which held 

 the coenosarc, are, of course, as vermicular in form as the 

 curvilinear thread of the coenenchyma, so that, in the decom- 

 posed fossil, where the same change takes place as that men- 

 tioned in the rectilinear structure, a vermicular form makes 

 its appearance in opaque white calcite, which in the unde- 

 composed lapidification was transparent, while hardly any thing 

 but a brown stain remains of the formerly white curvilinear 

 structure; in short, as before stated, the colouring is reversed. 



While, however, as also before stated, these are the extreme 

 forms of the coenenchymal structure of Stromatopora, there are 

 intermediate and modified forms (always remembering, of 

 course, the influence that various kinds of lapidification may 

 produce) — such, for instance, as a condensation of the hori- 

 zontal layer of the rectilinear structure in the finer species, 

 wherein the ends of the rods are so expanded that the straight 

 lines between them can hardly be seen, and the interstices 



