The snail in the middle with the aperture of its shell sealed with an operculum is Pomatias elegans.    From Wordnik.com.  [Archive 2009-09-01] Reference

In the case of P. elegans, the foot has to come out first to move the operculum, which is attached to the foot, out of the way.    From Wordnik.com.  [Archive 2008-03-01] Reference

Ammonites had an operculum (pl. opercula) as well.    From Wordnik.com.  [French masterclass] Reference

I've lost track. is a pulmonate family with an operculum.    From Wordnik.com.  [Assiminea succinea] Reference

The operculum is partially visible right behind the foot.    From Wordnik.com.  [Archive 2006-06-01] Reference

SNAIL'S TALES: Assiminea succinea and her operculum skip to main.    From Wordnik.com.  [Assiminea succinea] Reference

The picture on the left shows the operculum within the bodywhorl.    From Wordnik.com.  [Archive 2006-06-01] Reference

Unfortunately, your photos do not show whether it has an operculum.    From Wordnik.com.  [Assiminea succinea] Reference

The arrow points at the edge of the operculum of Hendersonia occulta.    From Wordnik.com.  [Archive 2006-11-01] Reference

The operculum and parts of the snail's foot are visible within the aperture.    From Wordnik.com.  [Archive 2008-06-01] Reference

I lifted the circular operculum from its place and laid it carefully on the bale.    From Wordnik.com.  [First Men in the Moon] Reference

The capsule opens explosively in dry weather, the operculum and spores being thrown to.    From Wordnik.com.  [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 "Brescia" to "Bulgaria"] Reference

Their description notes both the presence of an operculum and the location of the eyes.    From Wordnik.com.  [Archive 2008-03-01] Reference

But why does H. concavum, which doesn't have an operculum, have to put its foot out first?.    From Wordnik.com.  [Archive 2008-03-01] Reference

Stegocarpi according to the absence or presence of an operculum is thus clearly artificial.    From Wordnik.com.  [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 "Brescia" to "Bulgaria"] Reference

Drawing of retracted Cerithidea scalariformis showing the operculum and the pallial eye pse.    From Wordnik.com.  [Cerithidea] Reference

The capsule, the wall of which bears rudimentary stomata, has a small operculum but no peristome.    From Wordnik.com.  [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 "Brescia" to "Bulgaria"] Reference

These are all nice clues indicating that the pulmonates evolved from an aquatic ancestor with an operculum.    From Wordnik.com.  [Assiminea succinea] Reference

Von Baer also confirmed Rathke's discovery of the operculum, assigning it, however, to the second gill-arch.    From Wordnik.com.  [Form and Function A Contribution to the History of Animal Morphology] Reference

When the tide is out, these snails withdraw into their shells, closing their apertures with a soft operculum.    From Wordnik.com.  [Archive 2006-06-01] Reference

For they all from their very birth have an operculum to protect that part of their body which is exposed to view.    From Wordnik.com.  [On the Parts of Animals] Reference

These are the bones connected with respiration -- the operculum, the branchiostegal rays, the branchial arches, and others.    From Wordnik.com.  [Form and Function A Contribution to the History of Animal Morphology] Reference

The capsule does not open by an operculum but by four or six longitudinal slits, which do not reach either the base or apex.    From Wordnik.com.  [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 "Brescia" to "Bulgaria"] Reference

The central region extending between the apophysis and the operculum is composed of sterile tissue and forms the columella (c).    From Wordnik.com.  [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 "Brescia" to "Bulgaria"] Reference

He described growing out from in front of the first slit a structure which he compared to the operculum or gill-cover of a fish.    From Wordnik.com.  [Form and Function A Contribution to the History of Animal Morphology] Reference

And finally, the 3rd clue, which is even harder to notice, is that this snail has an operculum that it uses to close its aperture.    From Wordnik.com.  [Archive 2006-11-01] Reference

A distinct operculum is usually detached by the help of the annulus, and its removal may leave the mouth of the capsule widely open.    From Wordnik.com.  [Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3 "Brescia" to "Bulgaria"] Reference

As is the case for other trematode eggs, Fasciola eggs have an operculum (a distinguishing feature) on one end and are oval in shape.    From Wordnik.com.  [Chapter 2] Reference

The pallial eye is easy to notice when the snail lifts its operculum up and starts to come out of its shell with the aperture facing up.    From Wordnik.com.  [Cerithidea] Reference

From the hinder edge of the second visceral arch there develops, as Rathke had seen, a fold which is comparable with the operculum of fish.    From Wordnik.com.  [Form and Function A Contribution to the History of Animal Morphology] Reference

Presence of an operculum obliterating the medullary c.    From Wordnik.com.  [Recently Uploaded Slideshows] Reference

Whelk: cut off its head and tail, throw away its operculum, mantle, &c.    From Wordnik.com.  [Early English Meals and Manners] Reference

Ventral view of a later tadpole. op., the operculum. int., coiling intestine.    From Wordnik.com.  [Text Book of Biology, Part 1: Vertebrata] Reference

The distinct operculum in most of the figures would preclude their representing a shark.    From Wordnik.com.  [Animal Figures in the Maya Codices] Reference

There is a certain powerful shell-fish, called the Sazayé, with a very strong operculum.    From Wordnik.com.  [Tales of Old Japan] Reference

Reil, and the operculum were very small, corresponding to the inability to learn to speak.    From Wordnik.com.  [The Mind of the Child, Part II The Development of the Intellect, International Education Series Edited By William T. Harris, Volume IX.] Reference

Head of still later tadpole in horizontal section to show atrial chamber formed by operculum.int. g., internal gills.    From Wordnik.com.  [Text Book of Biology, Part 1: Vertebrata] Reference

Whelk: cut off its head and tail, throw away its operculum, mantle, &c., cut it in two, and put it on the sturgeon, adding vinegar.    From Wordnik.com.  [Early English Meals and Manners] Reference