Dr. O. J. ffinde — Western Australian Fossils. 201 



they dichotomize (Plate VIIIa. Fig. 5). They are of a hard, greyish 

 limestone, completely weathered out of the matrix ; but the tubular 

 cells and interstitial vesicles are partly infilled with chalcedony, and 

 in part with calcite. 



The outer surface of the branches is divided into irregular 

 polygonal areas by raised lines or ridges, sometimes scarcely visible 

 without a lens, at othei's elevated above the surface so as to form 

 margins to depressed areas (Figs. 5, 5c). These ridges are given 

 off from the angles of a zig-zag line, having a generally vertical 

 direction on the narrow sides of the branch. The ridges pass in- 

 differently across the cell areas and the macula?, but they frequently 

 meet in the centre of these latter. In weathered specimens these 

 ridges are not recognizable, and they are not often visible in sections, 

 unless tangential, where they appear as rows of bead-like dots, 

 with dark centres and lighter borders, not unlike the spines in 

 Monticuliporoids. 



The surface of the branches is dotted over with maculae ; these 

 are- oval or subcircular spaces free from cells (Fig. 5); without 

 definite boundaries, from 2 to 3 mm. in width, and from 5 to 8 mm. 

 apart, from centre to centre. The macula? are usually even with the 

 general surface, though sometimes slightly below it. The general 

 surface of the branches, both of the macula? and of the areas between 

 the cell-mouths, is, when well pi'eserved, covered with microscopic- 

 ally minute blunted tubercles which appear to be solid and imper- 

 forate (Fig. 5c). As a rule, however, the branches are now smooth 

 and imperforate. 



The centre of the branches has a median lamina extending from 

 end to end, from which the cells are given off. This axial lamina is 

 double in character ; in thin sections it appears as a dark line with 

 a layer of lighter material on either side of it, the whole being about 

 •05 mm. in thickness. It seems to be quite imperforate (Figs. 5a, b). 



The cells (= autopores) in this species are relatively long tubes, 

 circular, elliptical, or oval in section (Fig. 5d) ; they commence their 

 growth on the central lamina as conical tubes, semi-elliptical in 

 section ; in the first stage they are recumbent on the lamina for a 

 distance of about -75 mm., they then curve abruptly outwards and 

 extend directly to the surface, to which they open nearly at right 

 angles (Fig. 5b). The cell-walls are distinct from the interstitial 

 substance, imperforate, of an even thickness throughout their length, 

 not thickened near the surface, and in their upper portions apparently 

 of concentric fibres. At irregular intervals, from '25 to '75 mm. 

 apart, they are partitioned by complete tabula? (Fig. 5b) ; but they 

 are not infilled in any way with sclerenchyma. Measured in trans- 

 verse section, the cells are from # 2 to *25 mm. in diameter, but a few 

 of the larger ones on the borders of the macula? are - 37 mm. wide. 

 The cell-walls are from "03 to *05 mm. in thickness ; in some 

 instances they exhibit a decided thickening or lip at one side ; this is 

 of a more opaque character than the rest of the wall (Fig. 5c). 

 Beyond this thickening, there are no projections of the lip-margins 

 within the cell or distinct trifoliation of the cell itself, as in many 



