MINUTE STRUCTUEE OE STEOMATOPORA AND ITS ALLIES. 221 



The entire structure of the fossil, as viewed in vertical sections, re- 

 sembles that of a Cystiphyllum; but the vesicles are so minute that iu 

 merely polished slices the hand-lens will hardly reveal any structure at all. 

 In its general characters the fossil resembles that usually labelled 

 Stromatopora striatella, D'Orb. ; but it is densely and closely vesicular 

 in structure, and the examination of thin sections with the microscope at 

 once shows its entire distinctness from Stromatopora proper. 



Form. 8f hoc. — Common in the Clinton formation of Yellow Springs, 

 Ohio (infiltrated with dolomite) ; not so common in the Niagara Lime- 

 stone of Thorold, Ontario. Upper Silurian. Coll. Nicholson. 



Clathrodictyon CELLULOSUM, Nich. & Murie. 



Spec, char. — Skeleton forming irregular masses or thick expansions, 

 which attain a considerable size. Horizontal laminae about four in 

 the space of one line, inflected so as to form complete or incomplete 

 partitions, which divide the interlaminar spaces into a number of 

 irregularly oval vesicles, of which about three occupy the space of one 

 line. Surface tuberculate or granulated, the tubercles apparently 

 occasionally perforated. 



This beautiful species was first discovered by our friend Mr. George 

 Jennings Hinde, who at once recognized its distinctness from previously 

 recorded forms, and pointed out the fact to one of the present writers. 

 All the specimens which we have seen are either actually silicified, or are 

 infiltrated with silica, the skeleton remaining in the latter case calcareous. 

 In excessively thin vertical sections, the walls of the vesicles of the mass, in 

 parts, present the appearance of being perforated by minute tubuli ; but 

 we have been unable to satisfy ourselves of the reality of this appearance, 

 though, if established, this would throw an important light upon some 

 questions as to the minute structure of the Stromatopoi'oids. 



Form. 8f hoc. — Common in the Corniferous Limestone (Devonian) of 

 Wainfleet, Ontario. Coll. Hinde and Nicholson. 



{d) Sttlodictton, Nich. & Murie. 



Skeleton composed of laminae and interlaminar spaces, the 

 latter crossed by radial pillars. The entire mass is supported 

 upon a system of vertical columns, vphich may be composed of 

 comparatively dense calcareous tissue, or may, in other cases, be 

 loosely reticulated, and vs^hich are occasionally occupied by vertical 

 canals. Eound these vertical columns tbe horizontal laminae and 

 interspaces are concentrically arranged in successive layers ; and 

 the more or less extensive spaces between these are filled up with 

 reticulated tissue disposed in horizontal layers or irregularly. 

 Eadiatiug water-canals may or may not be present. 



Type. — Stylodictyon {Syringostroma) columnare, Nich. 



16* 



