The species found in the Sussex Chalk, [Lign. 138, fig. 2], is characterized by the longitudinal striæ on the outer surface. In some examples there is an external longitudinal furrow, and a corresponding internal ridge.[389]
[389] The specific name is in honour of Dr. George Morton, of Philadelphia, author of the "Synopsis of the Cretaceous Group of the United States."
The Sphærulites sometimes occur in groups in the Sussex chalk; I had a large water-worn mass, consisting of five or six individuals, anchylosed together. Some beautiful specimens collected by the late Mr. Dixon from the Chalk, near Worthing, are now in the British Museum.[390] The structure of the Sphærulite is accurately delineated in [Lign. 138, figs. 2a 2b.] The cavities of these shells are occasionally filled with flint, but in general with chalk, which may be entirely cleared away, as in fig. 2. The Hippurites of the limestone of the Pyrenees are frequently occupied by calcareous spar, and the substance of the shells is occasionally transmuted into the same mineral.
[390] Petrifactions, p. 468.
MOLLUSKITE.
Molluskite; or the carbonized remains of the soft parts of mollusca.—Before proceeding to the consideration of that numerous and important division of the mollusca the Cephalopoda, I will offer a few remarks on a carbonaceous substance resulting from the gelatinous matter of which the soft bodies of these animals are composed, and for which I have proposed the name of molluskite, to indicate its nature and origin.
Lign. 139. Coprolites and Molluskite. Chalk and Greensand.