56 J. W. DAWSON ON THE MICROSCOPIC 
a reticulated texture. Stromatocerium of Hall is a synonym. The 
genus ranges from the Upper Cambrian to the Devonian inclusive, 
and it is not easy to separate the species which have been described. 
2. Caunopora (Phillips, 1841).—The typical species, C. placenta, 
is defined by Phillips as ‘‘amorphous,” composed of concentric or 
nearly plane masses perforated by flexuous or vermiform small 
tubuli and by larger straight subparallel or radiating open tubes, 
persistent through the mass. This definition includes those species 
with simple tubes giving origin to radiating tubuli passing through 
the thickened laminz. Canostroma (Caunopora) incrustans of Hall 
is a typical American species, as is also Caunopora hudsonicaw above 
referred to. 
3. Ceenostroma (Winchell, 1867).—-This genus, as defined by its 
author, includes those species in which the radiating tubes diverge 
from the surfaces of little eminences raised in the concentric lamelle ; 
but, as Hall has well remarked, the presence or absence of eminences 
is a trivial character. The real distinction should be based upon the 
absence of the central simple radiating tubes, which in these species 
are represented by a group of more or less divergent ascending 
tubuli, so that the surface of the last layer presents eminences not 
with a single large pore at the summit, but with several small pores 
diverging from their sides. My Conostroma galtense above referred 
to and Hall’s Caunopora (Conostroma) planulata are typical forms. 
I have been obliged to reverse the generic names as used by Hall, 
in the twenty-third Report of the Regents of New York, in the 
manner above stated, as Phillips’s name certainly applies to the 
species with sengle vertical tubes. 
- Stromatopora nodulata of Nicholson (Ohio Report, vol. ii.) pro- 
bably belongs to this genus. 
4. Syringostroma (Nicholson, 1875).—This genus is defined by 
the author as composed of concentric lamine and vertical pillars 
which are so thickened and so amalgamated with one another as to 
leave nothing but the most minute rounded cells. Laminated tissue 
traversed by numerous large irregularly disposed horizontal canals. 
The species S. densa included under this genus in the Ohio Report 
is undoubtedly to be referred to Conostroma as above defined, being 
a species with the vertical tubes small and the radiating tubes very 
large. The species S. columnaris has, however, a very special cha- 
racter in the apparent want of vertical tubes, and in the coalescence 
of the laminee along certain vertical lines, giving solid columns ter- 
minating in imperforate or microscopically perforate tubercles at the 
surfaces. 
5. Dictyostroma (Nicholson, 1875).—In this genus the upper sur- 
face of each lamina is developed into conical points which support 
the lamina above instead of pillars. The lamine have horizontal 
canals, and the upper surface is apparently solid, though, no doubt, 
minutely perforate ; the irregular oscula referred to by Nicholson 
are probably accidental. D. undulata, Nicholson, is the typical 
species; but I think we may add to these several others in which 
