shells, and, in a few cases, an internal apparatus of the nature of shell, form the only evidence of the former existence of the myriads of these creatures that occupied the ancient waters.
The enduring nature of the calcareous coverings which these animals had the power of secreting, has placed our knowledge of Fossil Shells almost on a footing with that of recent Conchology. But the plan of our present inquiry forbids us here to take more than a general review of the history, and economy of the creatures by which they were constructed.
We find many and various forms, both of Univalve and Bivalve shells, mixed with numerous remains of Articulated and radiated animals, in the most ancient strata of the Transition period that contain any traces of organic life. Many of these shells agree so closely with existing species, that we may infer their functions to have been the same; and that they were inhabited by animals of form and habits similar to those which fabricate the living shells most nearly resembling them.[1]
All Turbinated and simple shells are constructed by Mollusks of a higher Order than the Conchifers, which construct, Bivalves; the former have heads and eyes; the Conchifers, or constructors of bivalves, are without either of these important parts, and possess but a low degree of any other sense than touch, and taste. Thus the Mollusk, which occupies a Whelk, or a Limpet shell, is an animal of a higher Order than the Conchifer enclosed between the two valves of a Muscle or an Oyster-shell.
Lamarck has divided his Order of Trachelipods[2] into two
- ↑ See Mr. Broderip's Introduction to his Paper on some new species of Brachipoda, Zool. Trans., vol. I., p. 141.
- ↑ This name is derived from the position of the foot, or locomotive apparatus, on the lower surface of the neck, or of the anterior part of the body. By means of this organ Trachelipods crawl like the common garden snail (Helix aspersa.) This Helix offers also a familiar example of
