Lower Silurian,
Tennessee. (After Ferdinand Roemer.)]
The most abundant, and at the same time the least understood,
of Lower Silurian Protozoans belong, however, to the genera
_Stromatopora_ and _Receptaculites_, the structure of which can
merely be alluded to here. The specimens of _Stromatopora_ (fig.
38) occur as hemispherical, pear-shaped, globular, or irregular
masses, often of very considerable size, and sometimes demonstrably
attached to foreign bodies. In their structure these masses consist
of numerous thin calcareous laminae, usually arranged concentrically,
and separated by narrow interspaces. These interspaces are generally
crossed by numerous vertical calcareous pillars, giving the vertical
section of the fossil a lattice-like appearance. There are also
usually minute pores in the concentric laminae, by which the
successive interspaces are placed in communication; and sometimes
the surface presents large rounded openings, which appear to
correspond with the water-canals of the Sponges. Upon the whole,
though presenting some curious affinities to the calcareous Sponges,
_Stromatopora_ is perhaps more properly regarded as a gigantic
_Foraminifer_. If this view be correct, it is of special interest
as being probably the nearest ally of _Eozooen_, the general
appearance of the two being strikingly similar, though their
minute structure is not at all the same.
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