1868.] DAWSON — EOZOON CANADENSE. 313 



narrowing; and in the middle of the narrow portion, a part has 

 the chambers obliterated by a white patch of carbonate of lime, 

 below which some of the septa are bent downward in the middle. 

 This is probably an effect of mechanical injury, or of the inter- 

 ference of a calc-spar vein. 



With the exception of the upper part above referred to, the 

 septa are seen to curve downward rapidly toward the margin, and 

 to coalesce into a lateral wall, which forms the defined edge or 

 limit of the fossil, and in which there are some indications of 

 lateral orifices opening into the chambers. It is worthy of remark 

 that, in this respect, the present specimen corresponds exactly 

 with that which was originally figured by Sir W. E. Logan in the 

 ' Geology of Canada,' p. 49, and which is the only other specimen 

 that exhibited the lateral limit of the form. 



On the side next the matrix, the septa terminate in blunt edges, 

 and do not coalesce ; as if the organism had been attached by that 

 surface, or had been broken before being imbedded. 



2. Microscopic characters.— Under the microscope, with a 

 W power, the margins of the septa appear uneven, as if eroded or 

 tending to an acervuline mode of growth ; but occasionally the septa 

 show a distinct and regular margin. For the most part merely 

 traces of structure are presented, consisting of small parts of canals, 

 filled with the dark colouring-matter of the limestone. In a few 

 places (PI. HI. fig. 1), however, these appear as distinct bundles, 

 similar to those in the G-renville specimens, but of fine texture. 



[In fig. 2 is represented a portion of the canal system in a 

 Grenville specimen, in which the canals, which are transparent in 

 one side (being infiltrated with carbonate of lime only) are seen 

 on the other to be partially filled with black matter, probably a 

 carbonaceous residuum of the sarcode which they originally con- 

 tained.— W. B. C] 



In a few rare instances only can I detect, with a higher power, 

 in the margin of some of the septa, traces of the fine tubulation 

 characteristic of the proper chamber wall of Eozoon. For the 

 most part this seems to have been obliterated by the infiltration 

 of the tubuli with colourless carbonate of lime, similar to that of 

 the skeleton. 



In comparing the structure of this specimen with that of those 

 found elsewhere, it would appear that the chambers are more con- 

 tinuous, and wider in proportion to the thickness of the septa, and 

 that the canal-system is more delicate and indistinct than usual. 



