412 Mr. H. J. Carter on Calcareous Hexactinellid 
XLVIU.—On Calcareous Hexactinellid Structure in the De- 
vonian Limestone ; large Fossil Hydrozoic Coralla from the 
Chalk ; and further Observations on the Replacement of 
Stlex by Calcite. By H. J. Carter, F.R.S. &e. 
On the shores of Teignmouth and Dawlish, in Devonshire, 
just after the New Red Sandstone touches the Devonian Lime- 
stone of Torbay, the former contains a number of fragments 
from the latter, which, as the Red-Sandstone cliff yields to the 
approach of the sea, fall down upon the beach, and, becoming 
rounded by the action of the waves and sand, are at length 
picked up by the lapidaries, who, selecting those which present 
the prettiest structure, cut and polish them for sale. 
It was one of these which Mr. Sollas obtained at Dawlish, 
that he presented to me, I think, in the summer of 1875, and to 
which I have alluded as presenting a structure which, “ dike all 
the rest of the Stromatopore, requires to be studied in all its 
bearings before a correct opinion can be obtained of its original 
nature’ (‘ Annals,’ 1877, vol. xix. pp. 72, 73); but since 
the possibility of silex being replaced by calcite during fos- 
silization has been established, and I have, through the great 
kindness of Prof. Zittel, received many specimens of several 
fossil Hexactinellid sponges, and have become better acquainted 
with the structure of Stromatopora, I have come to the conclu- 
sion that, the polished pebble presents a hexactinellid structure, 
which, if not a sponge, was still not a Stromatopora. 
Mr. Sollas kindly gave me polished horizontal as well as 
vertical sections of the structure; and on looking out among 
Prof. Zittel’s specimens for that which is most like it, I find 
that, to all appearance, it is identical with Verrucocelia gre- 
garia (Quenst. et Zittel; Verrucocelia, Ktallon) (‘ Annals,’ 
1877, vol. xx. p. 503). The specimen is two inches in dia- 
meter, and appears to have been cut from a circular pebble 
about an inch in thickness. 
Having, however, lately visited my friend Mr. Vicary at 
Exeter, whose collection of sections.of Stromatopora (which 
were obtained by a gentleman from the locality mentioned, 
during a residence of twenty-five years in the neighbourhood 
of Teignmouth) consists of between three and four hundred 
specimens, I found two among them possessing this hexac- ~ 
tinellid structure, but slightly modified; that is, the vertical 
lines in the vertical section are larger and more evidently 
hollow, but with no tabule or transverse septa, while here 
and there, on the horizontal section, are intervals tending to 
a stellate arrangement resembling the like in Stromatopora. 
Still here the resemblance ends ; for the coenosarcal skeleton 
