72 Cornish and Kendall—Calcareous Organisms. 
reference of the form to Teredo had been erroneous. In this view 
the late Dr. Gwyn Jeffreys concurred. The fossil has a sp. gr. of 
2-9, and is therefore composed of aragonite. We offer no suggestion 
as to its affinities. 
HExaAcoRALLA. 
All those corals examined by Mr. Sorby consisted entirely or 
almost entirely of aragonite. 
Parasmilia centralis.—The circumstances of the preservation of 
this coral in the Upper Chalk induced us to examine it, when we 
found that it was translucent, and therefore probably calcite. ‘This 
conclusion is confirmed by the sp. gr. 2°70. 
Ponyzoa. 
Mr. Sorby observes that many Polyzoa have a specific gravity 
intermediate between those of calcite and aragonite, and suggests 
that they may be composed of a mixture of calcite and aragonite. 
Observations by one of us on Polyzoa show that these two substances, 
as indicated by the translucency and opacity, are not actually inter- 
mingled, but, as we have found to be invariably the case in other 
organisms, occur as two distinct layers, inasmuch as many genera, 
such as Eschara, have, when well preserved, an outer opaque and an 
inner translucent layer, the former being absent in deposits from 
which the aragonite shells have disappeared. Here the disposition 
of the layers is the reverse of what is found in the Mollusca, which 
always have the aragonite layer internal. 
FoRAMINIFERA. 
Mr. Sorby has ascertained that certain of these (genera not speci- 
fied) are composed of calcite, but the facts we have accumulated 
regarding the group show that one great family, the Porcellanea, is 
similar in occurrence and behaviour to those structures characterized 
by the possession of aragonite tests. Moreover, the aspects of the 
tests, which have suggested the names Vitrea and Porcellanea, are as 
well shown in the fossil as in the recent state, and agree exactly 
with the aspect of calcite and aragonite shells respectively. Although 
we have not yet direct experimental proof that the Porcellanea con- 
sist of aragonite, yet it will be seen from what follows that they 
have been shown to be, relatively to the Vitrea, unstable towards the 
action of carbonated water. 
The form called Biloculina ringens occurs along with aragonite 
shells in the Coralline Crag of Gedgrave, and is the most abundant 
Foraminifer in that deposit; but at Aldeburgh, Iken, Sudbourne 
Cross Roads (Mrs. Sewell’s Pit), and the White Gates Pit, Sud- 
bourne Park (in the Coralline Crag from which the aragonite shells 
have been removed), there is not a trace of it; while the Poly- 
morphina frondiformis, comparatively rare at Gedgrave, is found here 
well preserved. 
In Prof. King’s “ Monograph on the Permian Fossils” (Palzont. 
Soc. vol. ii.) it is stated that no Imperforata Foraminifera are known 
from any formation below the Trias; but the most striking evidence 
