66 
And so it came to pass that these little fossils were bandied 
about from one class of the Animal Kingdom to another—some- 
times a Chiton, sometimes a Barnacle, and then a Crinoid—until 
the mystery has at length been cleared up, and that quite 
recently. It was only within the past year that the reproach 
was taken from these strange diminutive objects. M. Bepourn 
had, it seems, in 1868 actually found two casts of a fossil shell, 
a Neritopsis, with the so-named Peltarion in their mouths; and 
besides this, the keen research of an ingenious conchologist, 
M. Hierotyre Crosser, editor of the Journal de Conchyliologie, 
Paris,* materially assisted to clench the matter, for, by a close 
study of the opercula of the recent Gastropoda, he has clearly 
proved that the fossil puzzles, known under the name of 
Peltarion of the MM. Eupxrs-Drstonecuames, Problematica of 
Dr. QuenstEeDT, and Oliton radiatum of Mr. Moors, are simply 
the opercula of certain Gastropods belonging to the genus 
Neritopsis of the family Neritopside. 
A discussion of the following particulars may now engage 
our attention. Two points—one, the scientific relation of the 
operculum to the rest of the shell; and the other, its relation 
to the class of operculated Gastropods generally. There was a 
view—first conceived, I believe, by Apanson, and firmly held by 
the late Dr. Gray, so many years keeper of the Zoological 
department of the British Museum,—that the shell of a Gas- 
tropod with its operculum complete is the analogue of a bivalve 
Mollusc; or, otherwise expressed, that the operculum is the 
equivalent, zoologically, of the dextral valve of the Conchifera, 
This figment, so purely an imagination, consisted in fancifully 
regarding the simple shell of the Gastropod as a single valve, 
and its companion operculum as the corresponding valve of a 
bivalved Mollusc ; and it would, if only true, make our collections 
of the Gastropod Mollusca, for the most part, a mere array of 
single or odd valves. 
From this palpable reductio ad absurdum we feel relieved by 
the knowledge that malacologists of the foremost rank totally 
* Journal Conchyliol. Paris, 1875. pp. 57-66. 
