194 



BRITISH STROMATOPOROIDS. 



supposed minute coenenchynial tubes of P. ostiolata can be detected in properly 

 prepared thin sections. On the contrary, it is quite certain that the large tabulate 

 zooidal tubes of P. ostiolata are simply enclosed in a reticulated skeleton, the fibre 



Fig. 23. 



Fig. 23. — A. Part of a tangential section of Parallelopora ostiolata, Barg., from the Middle 

 Devonian Rocks of Biichel (Paflrath district), enlarged 80 times. B. Part of a vertical 

 section of the same, similarly enlarged. 



of which is traversed by dark and seemingly solid rods. It is quite probable that 

 these apparent rods are really the result of the infiltration with opaque matter of 

 a system of minute tubuli running in the interior of the reticulated skeleton-fibre ; 

 but it may be taken as altogether certain that such tubuli are part of the fibre 

 itself, and are in no way comparable with the interstitial tubes (" mesopores ") of 

 the Monticuliporoids or the " siphonopores " of the Heliolitidse. 



In Parallelopora, Ooldfussii, Barg., the appearances presented by the skeleton- 

 fibre, as seen in thin sections, differ considerably from those shown by corre- 

 sponding sections of P. ostiolata, though the differences observed may be 

 largely the result of differences in the mode of preservation, and in the 

 extent to which mineralisation has been carried. In a tangential section of a 

 well-preserved specimen of P. Ooldfussii (Plate XXV, fig. 4; and woodcut, 

 Fig. 24) the skeleton-fibre is seen to be thick, and to be completely reticulated, 

 while it exhibits in its substance numerous small round or oval spaces, which are 

 filled with clear calcite, and thus look like the apertures of transversely divided 

 tubuli. As the result of this, tangential sections acquire a characteristic perforate 

 or cribriform appearance (Plate XXV, figs. 4 and 8), which differs from the 

 uniformly porous aspect presented by corresponding sections of any species of 

 Stromatopora proper in so far that the apparent pores in the fibre are few in 

 number and comparatively large in size. Vertical sections of a well-preserved 

 specimen of P. Ooldfussii do not, however, show the presence in the fibre of 

 regular vertical tubules, such as would be inferred to exist from the phenomena 

 exhibited by tangential sections. On the contrary, such sections (Plate XXV, 



