310 Prof. H. A. Nicholson on some neio or 



and I shall reserve its description for the present *. The 

 remaining three species of Stromatoporoids described by the 

 above-named observers from the Devonian rocks of Iowa have 

 not come under my notice, and their microscopic structure has 

 unfortunately not been described or figured. The same is 

 true of various forms of Stromatoporoids described by Win- 

 chell and by Quenstedt from the Palaeozoic rocks of North 

 America. It is possible therefore that some of the forms which 

 I shall here describe as new may have been previously named 

 or figured. I have, however, elsewhere pointed out that 

 descriptions and figures of the merely macroscopic characters 

 of the Stromatoporoids are quite insufficient for the determina- 

 tion of species, and that, in point of fact, they only occasionally 

 suffice for the determination of the genus to which a given 

 specimen may belong. 



In connexion with one of the Canadian Stromatoporoids I 

 shall have occasion to describe a species of Stromatopora from 

 the Silurian rocks of Oesel ; but all the other forms dealt 

 with are North American. As in previous papers, I shall 

 confine myself principally to elucidating the microscopic 

 characters of the forms described, such characters being the 

 only ones upon which specific or generic distinctions among 

 the Stromatoporoids can be safely based. 



Stromatopora antiqua, Nich. & Murie. 

 (PI. VIII. figs. 9-11.) 



Pachystroma antiqua, Nicholson and Murie, Journ. Linn. Soc. ; Zool. 



vol. xiv. p. 223, pi. iv.figs. 2-5 (1878). _ 

 Stromatopora antiqua, Nicholson, Mon. Brit. Strom, p. 91, pi. v. figs. 8- 



11 (1886). 



Ccenosteum of considerable size, spheroidal or hemispherical 

 in form, with a limited basal attachment, and apparently 

 without an epitheca. The mode of growth is distinctively 

 latilaminar, the entire ccenosteum being made up of succes- 

 sively superimposed and perfectly definite strata, of which five 

 or six occupy the space of 1 centim. measured vertically. 

 The latilaminse are often more or less extensively separated 

 by minute intervals, and each consists of a single layer of 

 zooidal tubes. 



* I had previously conjectured (Mon. Brit. Strom, p. 95) that the fossil 

 which I had described from the Hamilton Formation of Ontario under 

 the name of Stromatopora nulliporoides (' Keport on the Palaeontology of 

 Ontario,' 1875, p. 78) might prove to be identical with the Ccenostroma 

 inerustans of Hall and Whitfield. I may, therefore, here state that an 

 examination of an authentic specimen of the latter has shown this con- 

 jecture to be correct, so that my name for the species must be abandoned. 



