viii PRErACE. 



been most unaccountably neglected even by Latreille, the 

 oreat founder of the modern school : we have therefore 

 thought it necessary to propose in this department many 

 new genera, and only have to regret that their definitions 

 could not be made more perfect without the destruction 

 of the specimens, frequently not our own, and which 

 therefore was unattainable : a more extended knowledge 

 of the natural affinities existing in this tribe, will alone 

 confirm or annul the propriety of these distinctions. 



In Couchology many of the genera long established on 

 the Continent, but new to our own collectors, have been 

 characterized and illustrated, as well as specific distinc- 

 tions defined between shells hitherto considered as vari- 

 eties; and here it must be observed that so much latitude 

 has been given to the meaning of the term ^variety, that 

 in its general acceptation its definition becomes im- 

 possible : our own idea of its true meaning is, a shell 

 possessing one or more characters which are changeable 

 and uncertain, and which consequently will not serve as 

 indications by which it may infallibly be distinguished 

 from all others ; xairietij depends on local circumstances, 

 and affects the size, colour, and greater or less develop- 

 mentof thesame modification of structure; a ^//etvY'.^ is per- 

 manent, its structure always the same though more or less 

 developed, producing and perpetuating its kind, and de- 

 pending on formation, discernible in youth, and matured 

 in age: we cannot therefore comprehend the contradictory 

 term oi permanent varieties in a state of nature (though 

 such occur in domesticated animals), which some authors 

 have used, and which has led to, in many instances, the 

 most erroneous conclusions. 



It is lamentable to see the opposition which is still 

 made by our own writers against all the modern improve- 

 ments ; yet although Linna3an Introductions to Concho- 

 logv are constantly issuing from the press, the desire of 

 being acquainted with a more natural and intelligible clas- 

 sification has already appeared; and as we are frequently 

 questioned on the subject, we cannot in this place do bet- 

 ter than refer the young student to the valuable article on 

 Conchology contained in the late su])i)lcment to the 



