Chcetetes in the Devonian Strata. — Rominger. 59 
I noticed that some differences existed between those from one 
locality and those from the other, and when I came to examine 
them microscopically, I found to my surprise more important 
differences in their structure than I had expected to find. 
The mode of growth in both is about the same, forming bulky 
convex masses or undulating thick tabular expansions, consisting 
of sub-parallel closely united tubules of about ^ of a millimeter in 
width; the surface exhibits low rounded monticules, on which or- 
ifices of somewhat larger size than the others present them- 
selves. 
In vertical fractures through such colonies is seen their compo- 
sition of a number of concentrically superimposed successive lay- 
ers, each of which represents a certain period in the growth, and 
a preceding and subsequent interruption of it. In this respect an 
obvious difference exists between the Sandusky and Louisville 
specimens. The concentric layers of the latter are merel}" indi- 
cated by an incrassation of the tube walls on that limit without an 
interruption in the continuity of their channels, while in the San- 
dusky form each concentric layer consists of an independent set 
of new tubes, which start with procumbent ends on the top of the 
orifices of a subjacent layer and soon after rise into an erect 
position. These procumbent basal ends of the new set of tubes 
frequentl}' are consolidated into a continuous lamina, which under 
favorable circumstances allows a separation from the subjacent 
belt of tubules, presenting a wrinkled surface, very much like the 
laminar surfaces we can observe on splitting the double leaved 
expan.sions of a Ptilodictya or Stictopora. Such periodical inter- 
ruptions in the growth occur at very variable intervals ; in the same 
specimens the thickness of such a layer may r>ot exceed two mill- 
imeters, subsequent ones may measure four and five millimeters, 
and some over an inch before a new disturbance in the growth 
commences. On cleaving such specimens vertically the tuliules 
readily separate so as to present their angular outlines intact and 
the surface partly covered with wall substances which on its sides 
exhibits delicate transverse wrinkles of growth, besides stronger 
corrugations becoming most conspicuous in the angles of junction 
between the neighboring tube channels. The specimens from 
Louisville, in distinction from the Sandusky specimens, never 
exhibit such transverse rugosities; their tubes join under remark- 
ably straight edges, but on the other hand, they show a plain 
