On the Stromatoporoids and Eozoon. 341 



XLV. — 0)1 the Stromatoporoids and Eozoon. 

 By E,. KiRKPATRICK. 



(Published hy permission of the Trustees of the British Museum.) 



[Plates VIII. & IX.] 



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

 the presence of siliceous spicules in t!ie k^tromatoporoids, 

 similar to those found in Merlia and MontlcuUpora, liad led 

 me to the conclusion that Stromatoporoids were Sponges. 

 I must now slate that I was misled to that conclusion, for it 

 has become evident to me that the supposed (spicules are 

 the calcified chitinous rings and half-rings belonging to the 

 canals and chambers of Foraminifera. 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, when 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 Moniiculipora [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 insuflSciently high 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 meshvvcrk of regular or irregular radial and concentrio 

 calcareous strands, these being really the edges of walls of 

 Foraminiftral chambers. 



The so-called 'Mabulse " are present in the usually darker 

 calcified soft tissues tilling the meshes or spaces not only 

 in S roniatcpora, but also in Actinostroma. Stromatoporoida 

 are found in the Ordovieian, Silurian, and Devonian strat?. 



