STRUCTURE OF STROMATOPORID&,. 57 
the thin lamine extend upwards in conical forms instead of pillars, 
and in some of which the laminz are thin and apparently destitute 
of the horizontal tubes. 
It is not impossible, though the specimens in my possession are 
not sufficiently perfect to render this certain, that Labechia conferta 
of Edwards and Haime, from the English Wenlock, may be allied to 
this or the last genus. 
[The above descriptions of Stromatoporidee were written before the 
publication of Nicholson and Murie’s excellent memoir in the Journal 
of the Linnean Society, which reached me only a few days before 
the proof of the above pages. Their descriptions of the structures, 
and views as to the classification and aflinities, agree in the main 
with those above given, and where they differ deserve careful consi- 
deration. They do not seem to have met with so good examples of 
the hollow pillars and perforated lamine as those I have described, 
nor to have so distinctly observed the relation of the horizontal 
canals to a supplemental deposit of calcareous matter. In their 
comparison with Parkeria too much importance is, I think, attached 
to the arenaceous character of that fossil—a character which we find 
in living Rhizopods associated with forms not dissimilar to those 
which are calcareous. It is also not improbable that some Stroma- 
toporide are built up of microscopic calcareous grains. Loftusia 
likewise presents points of comparison of some importance; and 
the Carboniferous species of that genus described and figured by 
Dr. G. M. Dawson (see p. 69) is especially instructive. In the 
memoir in question the genus Syringostroma of Nicholson is divided 
into Stylodictyon and Pachystroma, Stromatocerium of Hall is re- 
tained as a separate genus for some peculiar Stromatoporidee of the 
Lower Silurian, and a new genus (Clathrodictyon) is formed for 
vesicular species without pillars. The separation of forms contained 
in Syringostroma 1 have myself suggested above; and I think the 
grounds for retaining Stromatocertwn and adding Clathrodictyon 
may be sustained. The authors should, however, I think, have 
retained Ccnostroma of Winchell, and placed in it some forms 
which they have distributed in other genera. The new facts stated 
respecting Labechia are important with reference to that somewhat 
problematical fossil. | 
The geological distribution of the American Stromatoporide known 
to me may be stated as follows, though the species, no doubt, require 
some revision :— 
Potsdam formation .....1 6.00000. Stromatopora, sp. 
Trenton formation ......sc0cec00 Stromatopora rugosa, Hall. 
Dictyostroma? sp. 
petites ee se Stromatopora concentrica, Goldfuss, 
Coeenostroma constellatum, Hail, 
Caunopora hudsonica, n. sp. 
Dictyostroma undulatum, Nicholson, 
Guelph formation sessecovsereres Stromatopora ostiolata, NV. 
Cenostroma galtense, n. sp. 
Niagara formation 
