218 Frederick Ghapwmn; 



times vesicular, between the vertical partitions or undeveloped- 

 septa 15 . 



Whilst a peculiar tubular worm-like body is commonly found 

 at the base of the European and American forms, this has not 

 occurred in the Victorian species. On the other hand, many of 

 the specimens show an imprint of a crinoid stem firmly impressed,, 

 and in one; specimen of mudstone there are two small individuals 

 of this coral, each of which has affixed itself upon a small 

 Spirifer (S. cf. crispus) as a point d'appui. Numerous septa 

 are present in P. megastomum which are tuberculate or granulate,. 

 of a much coarser texture than that seen in P. problematicum 

 and other allied species 16 . 



The epitheca is strong in the Victorian species and concen- 

 trically wrinkled like the foreign forms, and is also radiately 

 marked with granulated lines. 



The Remarkable Development of Pleurodictyum in the Devon- 

 ian. — With the exception of the Victorian occurrence, this genus 

 is confined to the Lower and Middle Devonian in Western 

 Europe, Great Britain and North America. The question here 

 arises, should our Yeringian fauna be regarded as Devonian rather 

 than Silurian? It is true that several genera occurring in the 

 Yeringian seem to support this view, such as Phillipsastraea and 

 Michelinia, but on the other side of the argument, the evidence 

 of the gasteropods, trilobites and ostracoda is overwhelming. 



This constrains us at present to assume that certain forms of 

 life appeared amongst this Gotlandian and Wenlockian fades- 

 earlier than in the northern hemisphere, and migrated thence dur- 

 ing the transition period between the Silurian and Devonian- 

 epochs. 



Note on Allied Genera. — 



Cleistopora, Nicholson 17 . The genotype of this genus is Milne- 

 Edwards and Haimes Michelinia geometrical* . It is a Devonian 

 coral, discoidal, about 1.5 to 2cm. in diameter. It is said to 

 be generally parasitic on a brachiopod, and in this respect re- 

 sembles some Victorian specimens of Pleurodictyum herein men- 

 tioned. The short vertical corallites terminate in hexagonal 



15 Nicholson, in his "Tabulate Corals," p. 148, et seq., gives an ad- 

 mirable account of the structure of Pleurodictyum, based on sections taken 

 through the coralla of P. stylophorum. 



16. For further references to other species see Robinson, Trans. Con- 

 necticut Acad. Arts and Sci., Vol. XXI., 1917, p. 169. 



17. Geol. Mag., vol. V., 1888, p. 150. 



18. Polyp, foss. Terr. Pal., 1851, p. 252, pi. XVII., figs. 3, 3a. 





