176 Dr. M axon's and Mr. Rackett's 



1. Cochlea. 5. Patella. 



2. Nautilus. 6. Dent all urn. 



3. Cjipraa. 1. Concha. 



4. Jlal'totis. 8. Lepas. 



In some of the subsequent editions of the Si/stema two or three 

 more genera were added ; but, at length, in the 10th they were 

 augmented to thirty-two, wliich are only three less than Linniieus 

 employed on any oecasion afterwards. 'J'he edition of 1758 is, 

 therefore, to be considered as the period at which he may be said 

 to haAC perfected his principles of Testaceological arrangement, 

 though, in fact, the principles themselves underwent no material 

 change from the beginning, (a proof that our illustrious author 

 never treated the subject with carelessness,) the only alteration 

 that he deemed necessary being in the number of the genera : he 

 accordingly broke that of Cochlea into Conus, Bulla, Voluta, Buc- 

 cinum, Strombus, Marex, Trochus, Turbo, Ileliv, and Nerita, an<l 

 that oi Concha into Chiton, Fholas, and the bivalvia. The faults of 

 the Testaceological systems which preceded Linna^us's may l)c 

 readily deduced from the remarks made in various parts of this 

 paper. These systems laboured under extreme difficulty of ap- 

 plication, not only on account of the umltitude of divisions and 

 subdivisions which were deemed necessary by their respective 

 authors, but also of the practice of founding generic distinctions 

 on variations of general contour. Such variations being endless, 

 there was consequently no end to the multiplication of families, 

 and species became correspondently sparing. There was only one 

 author who can be said to be free from reproach on this score, 

 and that was Adanson : he, however, set out upon principles of 

 arrangement essentially different from those of the generality of 

 Avriters on this science, and, by making the contained animal al- 

 most exclusively the basis of his system, necessarily became 



limited 



