MOLLUSC A. 



CLASS I. MOLLUSCA. 



fnvertebral, soft, inarticulated animals, furnished with a more 

 or less prominent head at their anterior part. 



ARISTOTLE, the earliest writer on Natural History whose 

 works have reached the present time, is the first who employed 

 the term Mollusca, (MaXaxa,) although by it he designated on- 

 ly a part of the animals comprehended under the above defini- 

 tion. The ancient naturalists in general were but little ac- 

 quainted with these animals. They placed them among those 

 which they termed Exsanguia, corresponding to the Inverte- 

 bral Animals of modern naturalists, and divided them into two 

 sections, Mollusca and Testacea. Belon, Rondeletius, Aldro- 

 vandus, Johnston, and others, followed this method more or less 

 strictly in their different compilations. Owing to the great 

 beauty of the testaceous envelopes or shells of many of the 

 Mollusca, these envelopes were long collected by the rich and 

 curious as objects of interest from their colours and forms, while 

 the animals themselves were entirely neglected ; and although 

 Fabius Columna, Lister, Willis, Swammerdam, and others, de- 

 scribed the anatomical structure of many molluscous animals 

 with some degree of accuracy, yet, up to the time of Linnaeus, 

 it was never attempted to found a classification of them upon 

 considerations resulting from their general structure. 



In the last edition of his Systema Natures, Linnaeus, divid- 

 ing his class of Vermes into four orders, designated by the 

 names of Intestina, Mollusca, Testacea, and Lithophyta, ar- 

 ranged under the second of these orders several of the genera 

 destitute of calcareous envelopes, and in the third and fourth 

 divisions of his third order, Testacea, places those possessed 

 of shells. With respect to the latter, Linnaeus^s arrangement 

 is, for the most part, entirely founded upon the consideration of 

 the shell ; and although the structure of the shell may be con- 

 sidered as necessarily indicating a particular conformation in the 

 animal inhabitant, yet observations and dissections were not suf- 

 ficiently numerous at that period to enable him to form a clas. 



