MADREPORARIA PERFORATA. 



31/ 



Pleurodictyum, of different species and from widely remote regions. 

 There is little reason to doubt that it represents the tube of an 

 Annelide which lived as a ' ; commensal " with the coral, in the same 



Fig 200. — a. Lower surface of the cast of Plenrodictyum problonaticum, Goldf., from the 

 Lower Devonian of Germany, of the natural size (after Roemer), showing the vermiform body in 

 the centre ; b, A few of the separate casts of the tubes of Pleurodictyum problematicztm, Goldf.. 

 from the Devonian of the Eifel. showing the casts of the mural pores, enlarged (after Milne- 

 Edwards and Haime) : C. L'pper surface of the corallum of Pleurodictyum stylophoriim, Eaton, 

 from the Hamilton group of North America, of the natural size, showing the form of the calices 

 (Original) ; d, Lower surface of another example of the same, of the natural size, showing the stri- 

 ated epitheca, and the point where the corallum was attached to the stem of a Crinoid (Original). 



way as a Sipunculid (Aspidosiphoti) is found in constant association 

 with the corallum of the existing Heteropsammia. 



The genus Michelinia is in all its essential characters identical 

 with Pleurodictyum, but the corallum is massive (fig. 201), and the 

 tabulae are numerous, and inosculate so as to give rise to a tissue of 

 arched vesicles. The epitheca, also, commonly gives off root-like 

 processes of attachment. The species of Michelinia are all Devonian 

 and Carboniferous. 



It remains to briefly notice certain transitional types by which the Fav- 

 ositidce are connected with the Poritidce on the one hand and the Syrin- 

 goporidce on the other hand. Thus, a near approach to Alveopora among 

 the Poritidcp is effected by the remarkable Ordovician genus Calapcecia 

 ( = Colunuiopora)} The corallum in this genus is massive, and is com- 



1 An examination of the original specimens has clearly shown that the forms 

 described by Billings under the name of Calapcecia are identical with those 



