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Updated: May 25, 2025
As the weather became cold they always hibernated, closing the mouth of the shell with a thin, firm covering, or operculum, of chalk, which, mixed with their slime, made a substance like plaster of Paris.
Out of the hundred shells twenty-seven recovered. The presence of an operculum seems to have been of importance, as out of twelve specimens of Cyclostoma elegans, which is thus furnished, eleven revived. It is remarkable, seeing how well the Helix pomatia resisted with me the salt-water, that not one of fifty-four specimens belonging to four other species of Helix tried by Aucapitaine recovered.
It would be very hazardous to express an opinion as to the novelty or otherwise of the species and genera figured without the study of the specimens themselves, as the specific distinctions of fish are for the most part based upon character the fin-rays, teeth, the operculum, &c., which can only be made out by close and careful examination of the object, and cannot be represented in ordinary drawings however accurate.
With regard to the danger of too great reliance, I have a little tale to tell you. Be so good as to wake up from your drowsiness, and listen attentively. There is a certain powerful shell-fish, called the Sazayé, with a very strong operculum. Now this creature, if it hears that there is any danger astir, shuts up its shell from within, with a loud noise, and thinks itself perfectly safe.
He listened attentively to my brief rehearsal of the structure of parts whose names were still unknown to me: the fringed gill-arches and movable operculum; the pores of the head, fleshy lips and lidless eyes; the lateral line, the spinous fins and forked tail; the compressed and arched body.
His enormous head is now seen to be apparently circular in outline, and we readily see how perfectly it would fill the opening of the burrow like an operculum. But a close examination shows us that this operculum is really composed of two halves, on two separate segments of the body, the segment at the extremity only being the true head, armed with its powerful, sharp, curved jaws.
In every part one meets hermit crabs of more than one species, carrying on their backs the shells which they have stolen from the neighbouring beach. The large claws or pincers of some of these crabs are most beautifully adapted, when drawn back, to form an operculum to the shell, nearly as perfect as the proper one originally belonging to the molluscous animal.
Here the supposition at once presents itself that the primitive tubicolar worm was a Protula, that some of its descendants, which had already become developed into perfect Protulae, subsequently improved themselves by the formation of an operculum which might protect their tubes from inimical intruders, and that subsequent descendants of these latter finally lost the lateral filaments of the opercular peduncle, which they, like their ancestors, had developed.
The maoao is the turbo, a gastropod, a mysterious inhabitant of a twisted shell, who shuts the door to his home with a brightly-colored operculum, for all the world like half of a cuff-button. One eats him raw or cooked or dried. But he is not so odd as the varo one of the most delicious and expensive of Tahitian foods.
Some are of opinion that the two plates have been the gizzard of a cephalopod; others, that it may have formed a bivalve operculum of the same. Skeleton of Pterodactylus crassirostris. Oolite of Pappenheim, near Solenhofen. a. The celebrated lithographic stone of Solenhofen in Bavaria, appears to be of intermediate age between the Kimmeridge clay and the Coral Rag, presently to be described.
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