SECTION X. i8i 



with innumerable difficulties not eafy to 

 ibrmount. 



The feveral authors have formed their 

 methods from one fingle, or from a com- 

 bination of charafters ; but I rejeft all 

 the fyftems hitherto broached : and, as 

 I obferved, there {hould always be one 

 head charaQer, deduced from, the principal 

 or chief part of the obje£t, which charac- 

 ter fhould run through the whole fyftem, 

 to preferve a perfedt regularity ; I have 

 fixed on the aperture or mouth of the 

 Shell, for this head chara<3:er of my fyftem 

 or arrangement of turbinated Univalves. 

 The aperture or mouth will therefore be 

 the touch ftone of my families ; and the 

 fhapes, clavicles, colours, and works of the 

 Shells, I (hall ufe only as fubordinate 

 charadters. 



Having thus fixed the head or eflenlial 

 charaifter, I fhall begin with thofe Shells 

 that are the moft fimple, or leaff turbi- 

 nated, and very patulous, or almofl w^ide 



N 3 open ; 



