90 Dr. H. A. Nicholson on some 



tendency to regard the genus as being referable either to the 

 Foraminifera or to the sponges, or as constituting a connecting 

 link between these two orders of Rhizopoda. In the present 

 communication I propose to describe four new species of the 

 genus from the Silurian and Devonian formations of Western 

 Canada, all of which show certain points of relationship to the 

 Spongiida which have not been noticed in the species already 

 recorded by palaeontologists. 



1. Stromatopora ostiolata^Wich. PI. IV. figs. 1, 1 a. 



Spec. char. Fossil forming large hemispherical masses, 

 several inches in diameter, composed of innumerable delicate 

 lamina?, arranged concentrically, and separated by interspaces 

 which are broken up by numerous slender vertical pillars, 

 giving the whole a finely reticulate structure. The lamina? 

 are as thin as writing-paper ; and, with the intervening inter- 

 spaces, there are about ten of them in the space of one line. 

 The upper surface of the mass is undulated and is quite smooth, 

 except for the presence of small rounded or conical elevations, 

 perforated at the apex with rounded openings (PL IV. fig. 1 a) 

 and arranged with tolerable regularity in diagonal lines. 

 These elevations have a width of about half a line, and appear 

 to be of the nature of exhalant apertures or oscula. The lines 

 of oscula are placed at distances apart of from four to five 

 lines ; and the oscula in each line are about the same distance 

 from one another. When the mass is broken, similar osculi- 

 ferous surfaces are found to exist throughout the whole, ar- 

 ranged concentrically with one another, and separated by 

 spaces varying from two to three lines in thickness, these 

 spaces being occupied by the ordinary laminated or reticulated 

 tissue of the fossil. Laterally the lamina? and osculiferous 

 surfaces, instead of being concentrically arranged as regards 

 the entire mass, terminate in a series of rounded, nipple-shaped 

 prominences, each «of which is composed of thin concentric 

 lamina? which scale off like the coats of an onion. The lateral 

 surfaces of the fossil thus come to exhibit an extraordinary 

 nodulated and botryoidal appearance (PI. IV. fig. 1). 



It is impossible to give in a few words any adequate diagnosis 

 of this most remarkable fossil, which appears to throw con- 

 siderable light upon the affinities of the genus Stromatopora, 

 if, indeed, it does not truly constitute a new genus. In the 

 fact that its main bulk consists of a succession of thin calcareous 

 lamina?, with intermediate vertical props, pillars, or dissepi- 

 ments, marking off minute cellular compartments, S. ostiolata 

 agrees entirely with the typical species of Stromatopora ; and 

 in the great number of lamina? in a given space it closely 



