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Updated: June 11, 2025
The mouths of a large proportion of the marine univalves have these notches or canals, and almost all species are carnivorous; whereas nearly all testacea having entire mouths are plant-eaters, whether the species be marine, fresh- water, or terrestrial. There is, however, one genus which affords an occasional exception to one of the above rules.
We shall always find, that, in proportion as the functions are distinct, and, as it were, individualized by having special organs appropriated to them, animals rise in the scale of structure. The next class of Mollusks, the Gasteropods, or Univalves, with spiral shells, were numerous, but, from their brittle character, are seldom found in a good state of preservation.
For it is the science of life; and when the universal science touches the human life, it will have nothing less vivacious than this. It will have the particular of life here also. It will not have abstract revolutionists, any more than it will have abstract butterflies, or bivalves, or univalves.
Among many univalves agreeing with those of Africa on the eastern side of the Atlantic are Cypraea sanguinolenta, Buccinum lyratum, and Oliva flammulata. Amphistegina Hauerina, d'Orbigny. M. Alcide d'Orbigny has shown that the foraminifera of the Vienna basin differ alike from the Eocene and Pliocene species, and agree with those of the faluns, so far as the latter are known.
The terrestrial shells are all univalves. Many fossil species formerly referred to this genus, and which have been met with chiefly in marine formations, are now considered by conchologists to belong to Natica and other marine genera. Pleurotoma exorta, Brand. Upper and Middle Eocene. Ancillaria subulata, Sowerby. Barton clay.
Of the Silurian Univalves or Gasteropods there is not much to tell, for their spiral shells were so brittle that scarcely any perfect specimens are known, though their broken remains are found in such quantities as to show that this class also was very fully represented in the earliest creation.
Many of the univalves here at San Lorenzo were filled with, and united together by, pure salt, probably left by the evaporation of the sea-spray, as the land slowly emerged.
Trenham Reeks of the Museum of Economic Geology; it consists of carbonate of lime in abundance, of sulphate and muriate of lime, and of muriate and sulphate of soda. The carbonate of lime is obviously derived from the shells; and common salt is so abundant in parts of the bed, that, as before remarked, the univalves are often filled with it.
Thus, there are two species of Cypraea, one of Oliva, two of Mitra, four of the genus Cerithium, six of Fusus, two of Trochus, one of Patella, one of Emarginula, etc.; on the whole, more than thirty univalves, spiral or patelliform. At the same time, some of the accompanying bivalve shells, echinoderms, and zoophytes, are specifically identical with fossils of the true Cretaceous series.
Had it been declared that we are living in the Eocene epoch, the idea would not be so extravagant, for the great reptiles of the Upper Chalk, the Mosasaurus, Pliosaurus, and Pterodactyle, and many others, as well as so many genera of chambered univalves, had already disappeared from the earth, and the marine fauna had made a greater approach to our own by nearly the entire difference which separates it from the fauna of the Cretaceous seas.
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