STRUCTURE OF STROMATOPORID., - 53 
the columns the lamine are supported by pillars as in Stromatopora. 
They are also penetrated by horizontal canals which ramify radially, 
and are connected with vertical tubes as in Cenostroma, to which 
this form is very closely allied; I have seen only one species from 
the Corniferous Limestone, specimens of which have been kindly 
given to me by Dr. Newberry and Mr. Hinde of Toronto. 
Dictyostroma of Nicholson includes species in which the con- 
necting pillars are formed by upward bending of the lamine them- 
selves in conical points. The only species described by Nicholson 
(D. undulatum) is from the Niagara formation of Louisville, Ken- 
tucky. I have, however, seen an imperfectly preserved specimen 
with this structure from the Black-River Limestone of Port Claire. 
Mr. Hinde has sent me another from the Corniferous of Port Col- 
borne. These seem to be different from Professor Nicholson’s species 
in the distance between the lamine, which is much less than in the 
coarsely constructed species which he has described. The lamine 
are porous in these specimens; but I have seen no vertical tubes or 
oscula. 
The species Stromatopora compacta, from the Trenton Limestone, 
described by Billings, and which is not uncommon, does not appear 
to belong to this group of organisms. It consists of very minute 
hexagonal tubes with extremely thin walls and well-developed 
tabule, which, from their strong development and continuity, give 
in some specimens an appearance of concentric lamination. ‘The 
species seems to belong to the genus Stenopora, but its cells are 
excessively minute. Corals of the genus Mistulipora, with small 
tubes imbedded in a cellular coonenchyma, may readily, in certain 
states of preservation, be mistaken for Stromatopora. 
Stromatopore seem not unfrequently to have overgrown corals of 
different species ; and, in the case ot Syringopora, the tubes of these 
projecting through the mass often simulate oscula. Mr. Hinde in- 
forms me that, in the case of one species, this association is so com- 
mon that it suggests the idea of a case of ‘“ commensalism.” 
As connected with Stromatopora, it may be well to remark that 
some misapprehension still appears to exist respecting Archcwocy- 
athus, a fossil of the Cambrian rocks of Mingan, Labrador, and of 
which several species have been described by Billings. Of these the 
only one I have studied is A. profundus. ‘This is certainly a calca- 
reous, chambered organism, with pores connecting the chambers, and 
must have been the skeleton of a Rhizopod. The other species have 
similar structures. It is true, however, that on treating them with 
acids, billings obtained siliceous spicules in the matrix, which I have 
myself examined. I regard them as having belonged to lithistid 
sponges of the genus 7'richospongia of Billings, accidentally asso- 
ciated with the Archwocyathus. 
Some specimens of Stromatopora present remarkable lines of 
growth, caused by the appearance of two or three layers of smaller 
cells at intervals of seven or eight interspaces (Pl. LV. fig. 4). The 
preseryation of these without the intervening portions may, in some 
cases, account for the abnormally wide interspaces sometimes seen 
