Observations on the Opercula of some Silurian Gastropoda, &e. 
By Frepericx Smrruez, M.A., LL.D., F.G.S., &e. 
The operculate Gastropoda possess a shelly or horny cover, 
called an operculum, with which they close the mouth of their 
shell. This separate portion is developed on the posterior 
part of the foot, and when the animal has entirely withdrawn 
into the shell it constitutes in some degree a sort of defence or 
protection to the soft creature. We would now urge that a 
study of the operculum, be it recent or fossil, ought not to be 
disregarded by the naturalist. 
Agassiz, in his work on classification,* where treating of the 
succession and standing of animals, observes of the Gastropoda 
generally that— Every paleontologist is aware how imperfectly 
their remains have been investigated in comparison with what 
has been done for the fossils of other classes.” It is also the 
opinion of zoologists that not only the Gastropoda, but the whole 
of the Mollusca, need to be rearranged, as the present classifica- 
tion is only a disposition of so many artificial groups, and must 
be regarded as simply provisional until the Gastropoda are more 
thoroughly examined; wherefore, until that time arrive, we 
should studiously collect observations upon the subject, and 
even stray particles of information are not without value 
and significance. A collection of specimens of the operculate 
Gastropoda, whether land, fluviatile, or marine, without their 
opercula, loses much of its value, and avails little for the true 
purpose of natural classification. Such a collection is simply 
* « Bssay on Classification,” L. AGAssiz. Longmans, 1859. p. 163. 
