"But we are exceedingly interested about fossils," replied Charles; "pray do not pass any species that we may be likely to find."
"And I," said Lucy, "have much wished to ask whether the snake-stone ever was a shell? it is something like a Planorbis, but heavy and imperfect."
"I will answer your question presently," said her father. "Tell me what genera remain to be noticed among the univalves of Linnæus?"
"Argonauta and Nautilus," was the ready reply.
"The animals inhabiting these shells are Cephalopoda. The word indicates the position of the feet, or more properly arms of the animal, which are ranged round the head like a crown. The body is thick and fleshy, contained in a kind of bag, whence the head issues, surrounded by these arms, which vary in different genera.
CUTTLE-FISH.
BELEMNITE.
SPIRULA.
"The common cuttle-fish, a native of our seas, will give you an idea of a cephalopode.
"In the first family a fossil-shell occurs that is very frequently met with.
"Family, Orthocerata; genus, Belemnite, thunder-stone, or arrow-head. These fossil-shells occur abundantly in the chalk formations. Many superstitious notions have been attached to this extinct marine animal: of these you will find an account in the 'Penny Cyclopædia.'
"In the family Lituolita we meet with the delicate and remarkable little shell Spirula Peronii, distinct from Nautilus by the separation of the volutions: it is nearly covered by the body of the animal. The colour is white; the texture thin and brittle: it has a lateral syphon, the orifice of which is very clearly to be seen as each compartment is taken off. There is but one species; it is found in the Southern Ocean and the Moluccas. The shells are seen floating on the surface of the water when the animal is dead, and are sometimes carried to the shore. ([Plate 9.])