296 MOLLUSKS AND CONCHIFERS. 
ings which these anhnals 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 
enquiry 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 Uni- 
valve 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 re- 
sembling them.* 
All Turbinated and simple shells are con- 
structed by Mollusks of a higher Order than the 
Conchifers, Avhich construct Bivalves; the former 
have heads and eyes ; the Conchifers, or con- 
structors 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 MoUusk, which occupies a Whelk, or a 
Limpet shell, is an animal of a higher Order 
* See Mr. Broderip's Introduction to his Paper on some new 
species of Brachiopoda, Zool. Trans., vol. 1, p. 141. 
