38 BRITISH STROM A/TOPOROIDS. 



tubuli are visible, but the skeleton-fibre exhibits in tangential sections numerous 

 dark dots (Plate XI, fig. 5), and in long sections corresponding delicate dark lines. 

 It cannot be doubted that the different appearances presented by different 

 examples of this species depend upon the nature of the material which has served 

 as the infilling of the canal-system of the fibre, the tubuli being in the one case 

 filled with transparent calcite, and in the other with opaque oxide of iron. 



There are, however, still other cases in which the appearances presented by the 

 skeleton-fibre are more puzzling, though the phenomena just recounted would 

 seem to afford a key to their true nature. One of the cases in question is that of 

 Parallelojjora ostiolata, Barg., of which, through the kindness of Professor 

 Schliiter, I have investigated the original specimen. In tangential sections of this 

 singular type (Plate II, fig. 6) the skeleton-fibre is seen to be thick and reticulated, 

 and to be composed of nearly transparent carbonate of lime. Scattered through 

 the transparent fibre, and particularly abundant on its edges, are numerous 

 conspicuous dark dots, of oval, circular, or elongated shape, and of variable size. 

 Some of the dots show a minute ill-defined light centre, but they are mostly quite 

 opaque. In vertical sections of the same these dark dots are seen to be the cut 

 ends of minute rod-like bodies, which are prolonged vertically downwards, 

 running parallel with one another in the substance of the skeleton-fibre (Plate II, 

 fig. 7) in the intervals between the tabulate zooidal tubes. These rods are dark 

 and opaque, and are connected together at tolerably regular intervals by dark 

 horizontal lines, which constitute a series of horizontal or concentric laminae. It 

 seems to me that the most probable explanation of the appearances just mentioned 

 is that the dark rod-like bodies in the substance of the skeleton-fibre are really of 

 the nature of delicate tubuli filled up by some opaque material, and that the dark 

 cross lines by which they are connected together represent a system of horizontal 

 tubuli similarly injected. The phenomena previously alluded to as seen in thin 

 sections of Stachyodes verticillata, M'Coy, and Hermato stroma Schliiteri, Mch., 

 would entirely bear out this view of the subject. Moreover, this explanation is 

 further supported by an examination of one of the other species of Parallelopora, 

 viz. P. Goldfussi, Barg., of which I have also been able to examine the original 

 specimens. In this form the thick reticulated skeleton-fibre is seen in thin 

 sections to be traversed by numerous comparatively large vacuities or clear 

 spaces (Plate XI, fig. 9), which are bounded by dark tissue. These were regarded 

 by Bargatzky (' Die Stromatoporen des rheinischen Devons,' figs. 10 and 11) as 

 being so many vertical " coenenchymal tubes." In one sense this view is correct, 

 since these tubes were doubtless filled with organic matter during life ; but the 

 " coenenchymal canals " of this and other similar forms are, strictly speaking, the 

 much larger canals which place the different zooids in communication. The 

 tubuli of P. Goldfussi, Barg., do not, however, differ essentially from the still more 



