108 CALCISPHERA. 
possibility that they may have been the tests of some extinct 
form of protozoa - . . Whilst I am thoroughly satisfied 
that these objects are not Radiolarian, it is not easy to say 
what they are.” * 
The objections urged on the part of PRor. WILLIAMSON 
against their reception as Radiolaria would appear to be— 
(a) Their not possessing the fenestrated skeleton, which would 
have allowed the calcareous ooze to penetrate into the 
sphere cavity ; 
(6) That the structure is different from that of any existing 
Radiolarian ; 
(c) Inability to understand how the structure of a Silicious 
Radiolarian could be wholly replaced by Calcic Carbonate. 
(a) The interior of Calcisphera is filled with Calcite, says 
Pror. WILLIAMSON, “showing that in life it did not possess 
the reticulated. skeleton, or the interior would now have been 
filled with the surrounding ooze, and not with Calcite.” 
This statement as te the infiltration of ooze seems a very 
natural deduction, but unfortunately it is opposed to facts, 
which indicate that no absolute rule of this kind can be laid 
down. There is abundant evidence among the Carboniferous 
fossils to shew that (with every facility for entering) crystalline 
calcite, and not the surrounding matrix, now occupies the 
interior of many fossils. In this condition we find representa- 
tives of both Cephalopoda and Gasteropoda. Here there would 
be no obstacle to the ooze filling the interior. It doubtless was 
so filled originally, but has since been removed, and replaced 
with Calcite. The same thing occurs among the Polyzoa, par- 
ticularly with the Carboniferous Fenes/ella ; for even when this is 
found in black shale, the interior of the cell is found occupied 
with white Calcite. As Fenestella is closely allied to the 
Cyclostomatous Polyzoa, its open tubular cells would offer 
every facility for the infilling with the shale. As a matter of 
fact they are not so occupied. 
The interior of Calcisphera I find, as the result of extended 
observation, to be in some instances filled with Calcite, in 
others with the surrounding matrix, and the same is true of 
many Carboniferous fossils. 
Bearing the above in mind, I fail to see that the rule laid 
down by Pror. WitttAmson holds good, that if Calcsphera 
had possessed the open fenestration of the Radiolaria, the 
interior would have been filled, not as it is now with Calcite, 
but with the enveloping material. 
/b) That the structure of Calcisphera is different from that 
of any existing Radiolarian: I imagine that the absence in 
Calcisphera of the peculiar fenestration of the Radiolaria is the 
* Trans. Roy. Soc., pp. 523-525, Part II., 1880. 
