1872.] SOLLAS-UPPER-GREENSAND C0PR0LITES. 79
from their walls to their centres, thus forming a radiating mass of
crystals; it is well known that crystals arranged in this manner
will produce the phenomena described.
Behaviour with Hydrochloric Acid. — Hydrochloric acid dissolves the coprolites, some undergoing solution more readily than others, owing to their containing a larger quantity of calcic carbonate. While dissolving they emit a smell almost precisely resembling that of petroleum. The hydrocarbons which produce this odour must exist previously as gases, or combined with the calcic phosphate of the coprolite. I believe that they are present in the latter condition. The insoluble residue left on solution very frequently contains sponge- spicules and siliceous organisms; these may be separated in the same way as Foraminifera are obtained from a piece of chalk.
Enumeration of Genera*.
Genus 1. Rhabdospongia. Sponge more or less rod-like, 1" to 2" long, 1/3" to 1/2" diameter. Frequently attached at one end. Cloaca none, solid throughout. Spicules filiform, acerate, sinuous. Species: R. communis.
Genus 2. Bonneyia. Sponge cylindrical to clavate, size variable. Cloaca: longitudinal axis always occupied by a cloacal cavity from 1/3" to 2/3" of the whole diameter of the fossil. Spicules few. Species: B. bacilliformis, B. cylindrica, B. Jessoni, B. scrobiculata, B. verrongiformis.
Genus 3. Acanthophora. Sponge massive, lobose. Spicules acerate, fusiform, spiculated porrecto-ternate and recurvo-ternate, triradiate, hexaradiate. Species: A. Hartogii.
Genus 4. Polycantha. Sponge ovate. Cloaca present. Spicules acerate, defensive, triradiate, quadriradiate, hexaradiate. Species: P. Etheridgii.
Genus 5. Retia. Sponge cylindrical or hemicylindrical, marked on surface with a symmetrical fibre-like reticulation. Spicules few or absent. Species: R. simplex, B. costata.
Genus 6. Hylospongia. Sponge large and massive. Cloaca always present. Surface covered by a bark-like exterior, beneath which it is smoothly and longitudinally striated. Species: H. patera, H. calyx, H. Brunii.
Discussion.
Mr. Charlesworth complained that the author had not fully stated Dr. Bowerbank's views, which were founded on the fact that flint, wherever found, whether in fissures, the interior of organisms, or elsewhere, always presented under the microscope a reticulated structure. He had himself combated the view that flint was in all cases silicified sponge, and had demonstrated that certainly, in some cases, flint had been formed without the intervention of sponges; for in the case of the teeth in a lower jaw of a Mosasaurus found in the Chalk, he had found the pulp-cavities completely filled with
- Mr. Etheridge, after an examination of specimens, says that he entirely
approves of these generic groupings.
