96 BRITISH STROMATOPOROIDS. 



or oval black dots, which are scattered through the thickness of the fibre, but are 

 most abundant round the margins of the zooidal apertures. These dots have every 

 appearance of being solid, the use of a quarter-inch objective showing them to be 

 granular in texture and to have no distinct lumen. In vertical sections (Plate II, 

 fig. 7) the thick radial pillars are seen to separate vertical zooidal tubes, which are 

 crossed by well-developed transverse partitions or tabulae. The radial pillars are 

 further traversed by minute dark-coloured vertical rods, which run parallel to one 

 another and to the zooidal tubes, and which are connected at short intervals by 

 similar transverse rods, giving rise to a sort of ladder-like tissue. These rod-like 

 bodies appear to be solid, and the dark dots in the tangential section are their 

 transversely divided ends. 



Dr. Bargatzky (loc. cit.) considers these rod-like bodies to be the walls of 

 interstitial tubes occupying all the spaces between the larger tubes, and he regards 

 the transverse rods which connect these as being the " tabulse " of these interstitial 

 tubes. On this view the structure would be very much the same as that of such 

 Corals as Heliolites or Callopora. Tangential sections, however, show conclusively 

 that the dark vertical lines which run in the spaces between the ordinary zooidal 

 tubes, are not the walls of tubes, but that they are rods, and that they are contained 

 in the interior of a reticulated skeleton-fibre. I am therefore unable to accept Dr. 

 Bargatzky's views upon this point, though it is not possible to give an absolutely 

 satisfactory explanation of the nature of these curious structures. Two conjectures 

 might, in fact, be hazarded as to their nature. They have a general resemblance, 

 especially in vertical sections, to the radial pillars and their horizontal connecting- 

 processes as seen in the typical Actinostromai. We might therefore regard these 

 rods as being the radial pillars and " arms " of an Actinostroma persisting in the 

 general reticulate skeleton-fibre, a phenomenon which can be observed to a certain 

 extent in such forms as Stromatojwra Beuthii, Barg. On the other hand, a much more 

 probable hypothesis — and one supported by the observed phenomena in other cases — 

 is that these rod-like bodies are really of the nature of minute canals in the skeleton- 

 fibre, which have been injected with some dark-coloured and opaque material. 

 This conjecture is not absolutely incompatible with the former hypothesis, since 

 such canals might represent the axial tubes of a system of radial pillars and their 

 horizontal connecting-processes. On this view the structure of the skeleton in 

 Parallelopora ostiolata,Harg., would become comparable with that of Hermatostroma. 

 Or we might suppose the canal-system to be of the same type as the remarkable 

 tubulation of the skeleton-fibre in the genus Stachyodes, Barg., in which the tubuli 

 are sometimes filled with transparent calcite, or at other times are occupied by 

 opaque oxide of iron. It seems, however, hardly possible to arrive at final conclu- 

 sions as to the structure of Parallelopora until a more abundant material shall have 

 been collected and examined. 



