How would you explain this sentence? The fossil-shells of this district, and sorts of stone, such as have fallen within my observation, must not be passed over in silence. And first I must mention, as a great curiosity, a specimen that was ploughed up in the chalky fields, near the side of the down, and given to me for the singularity of its appearance, which, to an incurious eye, seems like a petrified fish of about four inches long, the cardo passing for an head and mouth. It is in reality a bivalve of the Linnaean genus of Mytilus, and the species of Crista Galli; called by Lister, Rastellum; by Rumphius, Ostreum plicatum minus; by D'Argenville, Auris Porci, s. Crista Galli, and by those who make collections cock's comb. How would you explain “have fallen within my observation” in the first sentence? PS: this extract is taken from The Natural History of Selborne. Thanks!By the way, how would you explain ‘s.' in "by D'Argenville, Auris Porci, s. Crista Galli"?