On the Stromatoporoids and Eozoon. 341 



XLV. — On the Stromatoporoids arid Eozoon. 



By R. KlRKPATRICK. 



(Publislied by permission of the Trustees of the British Museum.) 



[Plates Vin. & IX.] 



In a letter to * Nature,' Aug. 15, 1912, p. 502, I wrote that 

 tlie presence of siliceous spicules in the iStromatoporoids, 

 similar to those found in Merlia and MonticuUpora^ had led 

 me to the conclusion tiiat Stromatoporoids were Sponges. 

 I must now state that I was misled to tiiat conclusion, for it 

 has become evident to me that the supposed spicules are 

 the calcified chitinous rings and half-rings belonging to tiie 

 canals and chambers of Foraminit'era. It is now clearly 

 obvious also that the calcareous skeleton of Stromatoporoids 

 has a structure similar to that of the higher forms of 

 Perforate Foraminifera, 



It is not surprising that palaeontologists have failed to arrive 

 at a correct solution of the problem of the Monticuliporas, for 

 these organisms, wlien alive, exhibit extraordinary phenomena 

 without parallel elsewhere in biology, and wholly impossible 

 to understand without observing living specimens. Mo-t 

 fortunately the discovery of the living Monticulipora {Merlia) 

 normani off Porto Santo Island will enable me to explain 

 the real nature of the Palaeozoic examples. 



The Stromatoporoids, on the other hand, carry in them, 

 selves the clue to the problem they present, and it is at first 

 sight a little surprising that this clue has eluded the patient 

 search of so many investigators. This result was, I believe, 

 due to the use of insufficiently iiigh magnifying-powers. 



Stromatoporoids are commonly in the form of hemispherical 

 or cake-like masses, but they may be incrusting or digitate. 



The surface has a roughly granular aspect and presents 

 scattered stellate patterns (astrorhiza?). A vertical section (or 

 weathering of the edges) shows that the mass is built up of 

 concentric laminae or crusts. 



Slight magnification of a vertical section shows apparently 

 a meshwork of regular or irregular radial and concentric 

 calcareous strands, these being really the edges of walls of 

 Foraminiferal chambers. 



The so-called '-tabulae" are prcs;nt in the usually darker 

 calcified soft tissues filling the meshes or spaces not only 

 in Siromatopora, but also in Actinostromo. Stromatoporoiila 

 are found in the Ordovician, Siluiian, and Devonian strata. 



