AMMONITE.
NAUTILUS.
"Another family of this order, Nautilacea, contains, among many other genera, the celebrated Nautilus. This genus, you are already informed, is distinguished from Argonauta by its shells being many-chambered. Two or three fossil species have been found in London clay.
"Among the various fossil-shells abounding in different strata, not known in a recent state, the one most remarkable and frequently occurring is the Ammonite, Cornu Ammònis, so called from the resemblance it bears to the convoluted horns of Jupiter Ammon, in mythological history. This is your snake-stone, Lucy, a local name, which you had better change for Ammonite. Various legends are connected with this fossil, of which you may obtain information by consulting the before-mentioned publication.
"As you are desirous of studying geology, a knowledge of the Ammonites is very requisite, since whole sections of the genus are characteristic of certain strata.
"They are nearly allied to the Nautilus. The species are very numerous; one hundred and twenty according to some authors—two hundred and seventy species are enumerated by others. They occur in Europe, Asia, and America: they have been found in the chalk with a diameter of three feet.
"In the second division of this order the genus Argonauta occurs: the shell has been already described, and retains its original name. ([Plate 6.])
OCTOPUS.
LOLIGO.
SEPIA.
"In the third division is the family Sepiaria, containing Octopus, Lolìgo, and Sepia. This section contains animals without shells. Octopus vulgàris is common in the European seas. In hot climates it grows to a very large size. The animal has sufficient strength to draw a boat under water.
"Lolìgo also is found in our seas; the thin, transparent rib, called the dorsal blade, you may probably find on the shore, the flesh that covered the blade being cleared entirely from it. The colour is either white or brown. It is called sea-sleeve.
"The bone of the cuttle-fish, Sepia officinalis, is so frequently thrown on shore by the waves, that few persons visiting the sea-coast can be ignorant of its form. You have a large collection there I see, Lucy; and you are doubtless aware that this calcareous bone affords the pounce of the stationers, when finely pulverized: it also forms one ingredient of tooth-powder.