MEDINAN, NIAGARAN, AND CHESTER FOSSILS 
61 
expansions. These black dots tend to occur in rows, about 5 
or 6 in a width of 0.5 mm. Possibly these black dots locate 
extensions of some of the anastomosing fibers, and served as 
supports of very fine hair-like fibers, similar to those seen along 
the lateral margins of the fronds. This appears to be confirmed 
by some specimens in which some of the hair-like fibers extending 
beyond the margins of the lobes can be traced at their proximal 
ends to dots located some distance back from these margins, 
along the flat faces of the fronds. 
Similar hair-like fibers cover the surface of the dichotomously 
branching frond-like expansions occurring in the Cayugan of 
the Buffalo area of New York, and in the Kokomo formation of 
northern Indiana. These Upper Silurian frond-like expansions 
usually are referred to Buthotrephis, a genus originally described 
from the Chazyan and Trenton of New York. 
While it is customary to refer these Upper Silurian forms of 
Buthotrephis to the algae, it should be remembered that no 
evidence of structure within the frond or of characteristic forms 
of reproduction have yet been adduced in proof of this view. 
The black coloring of the specimens of Buthotrephis from the 
Buffalo and Kokomo areas usually is regarded as evidence of 
plant origin, the black coloring being regarded as being derived 
from plant material, like coal. However, it is exceedingly doubt- 
ful whether such minutel}^ fibrous structures as those here 
described in Leveilleites ever could have had a plant origin, con- 
sidering the perfection of their preservation. 
Under a microscope, the fibers of Leveilleites are seen to pass 
between the minute sand grains forming the matrix as though 
these fibers had some measure of stiffness at the time of their 
burial in the sea mud. Apparently they were more or less free 
from other material. 
These fibers resemble the fibers of sponges more than those 
of plants. However, even if of animal origin, the fronds of 
Leveilleites show no trace of oscula or of other characteristic 
structures of sponges. Possibly they belong to some group of 
animals not yet discriminated from those recognized so far. 
