22 . SHELLS AND SHELL-FISH. .PART I. 



(18.) As a purely conchological system, this was un- 

 questionably the best and the most original of any that 

 had appeared since the revival of learning. It was pub- 

 lished in 1797, nearly twenty years before the first of 

 Lamarck's volumes appeared. * That it was well known 

 to the latter can hardly be doubted, when we see no less 

 than ten genera similarly named by both ; and that 

 almost every genus of Lamarck's univalves are found in 

 this list, under different, but less classical, names. Of 

 univalves, Humphrey has 87, contained in the single 

 collection of which his book is a catalogue. How many 

 more he had determined to name, does not, of course, 

 appear ; but the total number of Lamarck's is but 96, 

 for the whole of the testaceous gastropods. 



(19.) Lamarck's system, so far as regards the animals 

 now before us, may be thus briefly stated. He arranges 

 the whole group under the two classes of I. Con- 

 chifera; and, II. Mollusca. The first contains the 

 bivalve shell-fish, and is again divided into two orders : 

 one of these is called Conchiferes dimyaires, the in- 

 terior of the shells presenting two muscular impressions, 

 separated and lateral; while in those of the second 

 order, or Conchiferes monomyaires, there is but one 

 muscular impression, placed nearly in the centre, the 

 muscle itself being single, and which appears to run 

 through the body of the animal. Each of these great 

 divisions of bivalves contains several others, denominated 

 sections, chiefly differing in the structure of their feet. 



ORDER I. CONCHIFITRES DIMYAIRES. 



