AXIAL TUBES. 57 



shall speak of the structures now in question as "astrorhizal tabulae." So far as I 

 have seen, these structures can almost always be recognised in thin sections of 

 Stromatopora ? dartingtonensis, Cart. ; but they are by no means peculiar to this 

 species. Similar structures in an equally well-developed form, occur in Stromato- 

 porella eifeliensis, n. sp., and they are present more or less commonly in various 

 other types. Even in those forms in which they may be said to be of constant 

 occurrence, they have, however, a very variable development, and they likewise 

 vary much in form. In most cases they have the form of complete calcareous 

 plates, which are placed at irregular intervals across both the larger and smaller 

 astrorhizal canals, but principally in the former (Fig. 7). They may be straight or 

 curved, or even funnel-shaped or vesicular, as, for example, they sometimes 

 are in Stromatoporella laminata, Barg. They doubtless indicate the periodically 

 produced lines of demarcation between the superficial and still active portions of 

 the colony and the deeper dead portions of the mass ; but it is difficult to assign to 

 them, with our present knowledge, any further function. 



(h) Axial Tubes. — In certain anomalous types of Stromatoporoids there occur 

 tubes which may be distinguished by their position and other characters from the 

 astrorhizal canals or the ordinary zooidal tubes. The tubes in question are of 

 large size ; they have a definite relation to the entire organism ; they are definitely 

 circumscribed by the general tissue of the coenosteum ; and they are usually, if not 

 always, intersected by distinct calcareous plates or " tabular." Except in the 

 presence of a thickened proper wall, the well-known tubes of the so-called 

 " Caunoporce " have very similar characters, and it might therefore have been 

 natural to consider the distinctive tubes of the forms included under the head of 

 Caunopora, Phill., and Diapora, Barg., in this place also. Many reasons have, 

 however, induced me to devote a special section to the consideration of these latter 

 fossils. The tubes to which I now specially refer, and which I shall distinguish by 

 the name of " axial tubes," are found, in their most marked form at any rate, only 

 in certain aberrant genera of Stromatoporoids, namely Idiostroma, Winch., 

 Amphipora, Schulz, Stachyodes, Barg., and Beatrices, Bill. The axial tube of the 

 last of these is, however, in many respects peculiar, and I need here only speak of 

 the three first-named genera. All these form, typically, cylindrical colonies, some- 

 times branched or multiple, sometimes simple, rooted basally, and having a general 

 resemblance to the dendroid species of Favosites or Pachypora. In the above three 

 genera, the cylindrical coenosteum is traversed by a large axial canal, which may be 

 single, or which may be accompanied by a small but variable number of lesser but 

 otherwise similar canals, running parallel with the main tube and at a little distance 

 around it. Both the axial tube and the smaller tubes (when the latter are present) 

 are definitely circumscribed, and have their internal cavities intersected by 

 transverse calcareous plates or " tabula?." These tabulae may run directly across 



