Mr. H. J. Carter on Stromatopora dartingtoniensis. 347 



fibre are all inflated at their point of contact, as shown at 

 fig. 4, b ; and on account of the undulating development of 

 the laminse the horizontal section (fig. 5), although generally- 

 presenting the curvilinear structure (fig. 5, a), sometimes 

 presents a punctate one (fig. 5, b), or a retiform one, as at 

 fig. 5, c, or a more compact curvilinear one, as at fig. 5, d, &c. 

 &c, owing to the section passing through the undulations at 

 slightly variable depths. 



Of course the above description of 8. dartingtoniensis , 

 having been taken from only a few specimens of the species 

 found in " Pit-Park Quarry," must be considered approxi- 

 mative, since it probably not only exists throughout the 

 Devonian Limestone of the neighbourhood, but may be found 

 to present itself under many more forms, both generally and 

 structurally, than those above mentioned. 



EXPLANATION OF PLATE XVIII. 



Fig. 1. Stromatopora dartingtoniensis, n. sp. Natural size. Incrusting 

 form, showing: — a, natural surface; b, broken surface; ccc, as- 

 trorhizse; d, union of ultimate branches of the astrorhizse ; e, ver- 

 tical section of the astrorhiza as it is developed upwards through 

 the structure of the Stromatopora ; f, ends of the brandies ob- 

 liquely cut by the section; gg, truncated ends of branches of 

 the astrorhizge as they appear in a vertical section of Stroma- 

 topora. 



Fig. 2. The same. Natural size. Massive form. Tracing of the plane 

 of fracture a a a a, showing the form, size, and arrangement of 

 the astrorhizse, whose branches are partially empty, all the 

 calcspar but the tabulse having been removed by r decomposi- 

 tion. 



N.B. As the branches of the astrorhizse are not on the same 

 plane, but generally dip downwards (fig. 1, f), their smaller 

 branches disappear in the horizontal section, and thus the larger 

 ones look in the delineation as if abruptly terminated. 



Fig. 3. The same. Astrorhiza of fig. 2, magnified about four diameters, 

 to show a, the tabulae. Diagram. 



Fig. 4. The same. Vertical section, to show the structure of the ccenen- 

 chyma, relatively magnified about four diameters, a, appear- 

 ance of the vertical rods and horizontal lines of the laminae as 

 they cross each other at nearly right angles, modified by slight 

 undulations ; b, portion showing their inflation at the point of 

 intersection ; c, portion in which the vertical rods are omitted 

 and the lines of the laminae only inserted ; d, large branch of an 

 astrorhiza ; e e, truncated branches of astrorhiza? as they appear 

 in the vertical section. Diagram. 



Fig. 5. The same. Horizontal section, to show the structure of the 

 ccenenchyma, relatively magnified about four diameters, a, cur- 

 vilinear appearance of the lines of the laminae when viewed 

 horizontally — sometimes, owing to the undulation of the lamina, 

 presenting a punctate appearance (b), or a reticulated one (c), or a 

 more compact curvilinear structure (rf) ; e, branch of astrorhiza. 

 Diagram. 



25* 



