The pretty wide thin inter-operculum lays freely over the gill membranes, and covers them when shut up.
"Discoveries in Australia, Volume 1." by J Lort Stokes
Cells furnished with a pedunculate operculum.
"Narrative Of The Voyage Of H.M.S. Rattlesnake, Commanded By The Late Captain Owen Stanley, R.N., F.R.S. Etc. During The Years 1846-1850. Including Discoveries And Surveys In New Guinea, The Louisiade Archipelago, Etc. To Which Is Added The Account Of Mr. E.B. Kennedy's Expedition For The Exploration Of The Cape York Peninsula. By John Macgillivray, F.R.G.S. Naturalist To The Expedition. In Two Volumes. Volume 1." by John MacGillivray
The shell is of a yellow horn colour (as is also the operculum) thin and transparent.
"Voyage Of H.M.S. Rattlesnake, Vol. 2 (of 2)" by John MacGillivray
This history was told me, and the nest with its operculum shewn me by the late Dr.
"Zoonomia, Vol. I" by Erasmus Darwin
There is no operculum.
"Marine Protozoa from Woods Hole" by Gary N. Calkins
The distinct operculum in most of the figures would preclude their representing a shark.
"Animal Figures in the Maya Codices" by Alfred M. Tozzer and Glover M. Allen
The capsule, the wall of which bears rudimentary stomata, has a small operculum but no peristome.
"Encyclopaedia Britannica, 11th Edition, Volume 4, Part 3" by Various
Anal operculum: the dorsal arch of the 10th abdominal segment; in caterpillars = supra-anal plate, q.v.
"Explanation of Terms Used in Entomology" by John. B. Smith
Genital orifice covered by an operculum.
"Encyclopaedia Britannica, 11th Edition, Volume 2, Slice 3" by Various
The shell consists of six plates, with an operculum of four valves.
"The New Gresham Encyclopedia. Vol. 1 Part 3" by Various