MOLLUSKS AND CONCHIFERS. 225 



shells, and, in a few cases, an internal apparatus of the 

 nature of shell, form the only evidence of the former exist- 

 ence 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.* 



All Turbinated and simple shells are constructed by Mol- 

 lusks 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 im- 

 portant parts, and possess but a low degree of any other 

 sense than touch, and taste. Thus the Mollusk, which oc- 

 cupies 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 Trachelipodsf into two 



* See Mr. Broderip's Introduction to his Paper on some new species of 

 Brachiopoda, Zool. Trans., vol, I., p. 141. 



t 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 gar- 

 den snail (Helix aspersa.) This Helix offers also a familiar example of 



