432 
Greensand Cherts*,” Mr. Bowerbank inferred that the sponges from 
which he conceives those bodies originated, differed from recent kera- 
tose sponges only in having possessed numerous siliceous spicula. 
Since that paper was read, the author, however, has found in true 
keratose sponges from Australia}, as well as in the sponges of com- 
merce from the Mediterranean and the West Indiest{, siliceous 
spicula in great abundance. All discrepancies, therefore, between 
the extinct and modern types of a portion of the animals under con- 
sideration, he says, is now removed. In these prefatory remarks, 
Mr. Bowerbank likewise states that there is at present only one 
known species of recent sponge (S. fistularis) the fibre of which is 
truly tubular. 
The author then proceeds to detail the evidences of the existence 
in moss agates from Oberstein and other parts of Germany, as well 
as from Sicily, and in green jaspers from India, of the remains of 
sponges, in the following order: lst, the proofs of the fibrous struc- 
ture; 2nd, of the preservation of gemmules; and 3rd, those of the 
existence of vascular structure. ‘The specimens were examined as 
opaque objects, with direct light concentrated by a convex lens. 
The number of agates amounted to nearly 200, and that of green 
Jaspers to about 70. 
1. Fibrous structure.—Though polished agates afforded Mr. Bow- 
erbank, in almost every specimen, strong evidence of spongeous origin, 
yet the structure and arrangement of the fibres were seldom per- 
fectly preserved throughout, presenting every intermediate state from 
complete decomposition to the most distinct spongeous tissue. The 
siliceous matrix of these remains exhibited a clear and frequently 
crystalline aspect, but the prevailing tint of the enclosed organic 
matter was bright red, brown, or ochreous yellow ; occasionally, how- 
ever, the fibre was milk-white or bright green. The colourimg mat- 
ter was generally confined within the bounds of the animal tissue, 
leaving its surface smooth and uninterrupted; sometimes it occurred 
only in the interior of the tubular fibre, the sides being semipellucid 
or milk-white ; whilst in other cases not only the fibre was com- 
pletely charged with colouring matter, but the surface was also 
shghtly encrusted with it. In an agate believed to be from Sicily, 
the greater part consisted of a confused mass composed of innume- 
rable bright red fibres with no perceptible remains of surrounding 
structure, but near the margin of the specimen the tubuli were as 
perfectly preserved as in a recent sponge, presenting a semi-pel- 
lucid and horny-looking substance enveloping red fibres. In those 
instances in which the red pigment did not appear to have entered” 
the tube, the structure was best preserved, and Mr. Bowerbank 
states that such ought to be the case, as the fibres of the Spongia 
jistularis, though hollow throughout, are closed near the natural ter- 
mination. The tubes in the Sicilian agate anastomosed in the same 
* See Geol. Trans., 2nd Series, vol. vi. Part 1. 1841. Proceedings, 
vol. ili. p. 278, 1840. 
+ Annals of Nat. Hist., April 1841. 
t Microscopic Journal, vo]. i. No. 1, p. 8, 1841. 
