54 R. P. Whitfield—Structure of Dictyophyton. 
passing in each direction obliquely across or between the longi- 
tudinal and horizontal sets, but not interwoven with them; 
so that the longitudinal series forms external ribs extending 
the length of the sponge, and the horizontal series inside ribs 
or bands, and they appear as if cemented to each other at their 
crossings. The oblique threads, besides strengthening the 
structure, cut across the angles of the quadrangular meshes 
formed by the two principal sets of fibers, and give to them 
the appearance of circular openings, making the structure 
much more complicated than in Dictyophyton. The addition of 
oblique fibers in Huplectedia is the most noticeable difference 
between the two forms; but if placed horizontally and longi- 
tudinally-between the primary sets they would produce pre- 
cisely the structure seen in Dictyophyton 
yet we have no positive evidence of the nature of the 
b 
A 
substance which composed the fibers in Dictyophyton. The 
only cases known, so far as I am aware, of the preservation of 
the substance of the fossil is that mentioned above, where the 
space between the matrix and the cast is occupied by a ferrugi- 
nous body, a material which so often replaces siliceous organ- 
isms in a fossil state, and specimens of D. Newberryi from Rich- 
field, Ohio, on which there occur slight patches of a carbonaceous 
substance, but not sufficient to warrant the conclusion that it 
ever formed a part of the structure, even in the opinion of the 
author of the genus who supposed these organisms to have 
been of vegetable origin ; especially as they are associated with 
numerous fragments of terrestrial plants. I am therefore led 
to the opinion, from their firmness of texture as evinced by the 
also figured in the 16th Report above cited, I think would 
also better conform to this idea than to that of a vegetable 
origin, although its broad flattened bands may be something 
of an objection. 
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