52 J. W. DAWSON ON THE MICROSCOPIC 
kindness of Mr. Selwyn, Director of the Geological Survey of Canada, 
a specimen collected by Professor R. Bell on the Albany River, 
Hudson’s Bay, in rocks of Upper Silurian age. In this specimen 
the skeleton remains as carbonate of lime, while the canals and tubes 
are in great part empty, so that their minute ramifications are in the 
condition of a recent specimen, and can be injected with colouring- 
matter. ‘The actual structures thus presented are as follows :— 
Lamine thin and obscure. Chambers almost entirely filled with 
supplemental deposit, traversed by innumerable microscopic hori- 
zontal canaliculi, which are tortuous and anastomose frequently. 
They are connected with systems of radiating canals which termi- 
nate centrally in vertical tubes traversing the whole thickness of 
the specimen, and opening at the surface in round pores visible to 
the naked eye and placed on the summits of slight eminences. The 
pores are about 4 millimetres apart horizontally. ‘The upper surface 
is smooth and does not show the radiating canals, but these are 
disclosed by erosion or by horizontal fracture. This species closely 
resembles Hall’s Cawnopora incrustans, from the Devonian of New 
York ; but the pores are more regular and less than half as far apart, 
and the radiating tubes are more numerous. For the above species 
I have anowaaxtad. the name Caunopona hudsonica (P1. LV. fig. 9 and 
1B, We ites IO) 
If ave described in a former publication* a fossil preserved in a 
similar way, but less perfectly, and which has vertical tubes in 
groups instead of singly ; it is trom the Galt Limestone of Ontario, 
and belongs to the genus Canostroma, as limited in the sequel. I 
would propose for it the name C. galtense. 
The structures in Caunopora and Cenostroma are unquestionably, 
at first view, more akin to those of sponges than are those of the 
typical Stromatopore, as the vertical tubes may be taken for oscula, 
and the extremities of the fine tubes for the incurrent pores. On the 
other hand, the solidity of the calcareous walls and supplemental 
thickenings is at variance with such a view ; aud in many respects 
they more nearly resemble Hozoon than any of the Palaozoic fossils 
with which I am acquainted. The canal-system in both is, indeed, 
so much alike that it would not be easy to distinguish it, except that 
Lozoon wants the continuous vertical tubes and possesses a true 
nummuline wall. 
The minute structures of such species as the Stromatopora nodu- 
lata of Nicholson (S. sanduskyana of Rominger, Pl. V. fig. 11), con- 
nect the true Stromatopore with the species of the genus Canostroma ; 
and these, by confluence of the separate tubes, pass into those of the 
genus Cawnopora. 
Of the species separated by Nicholson in the genus Syringostroma, 
that which he has named S. columnaris is a very peculiar type. It 
is penetrated vertically by what seem to be solid columns, and which, 
on microscopical examination, prove to result from upward bending 
and fusion of the lamine along certain vertical lines. The effect is 
obviously to give much additional strength to the skeleton. Between 
* ‘Life's Dawn on the Earth,’ p. 160. 
