TESTACEA. 19 



not form any part of the subjects to which my attention was originally 

 directed. I did not contemplate investigations of their nature. But as 

 it is rare for extensive fields of enquiry of long duration to be confined 

 within the bounds prescribed by any one to himself, accidental circum- 

 stances may bring important subjects under review. 



The figures of a few living shells, therefore, are represented here, 

 which is certainly the only suitable method of offering the Testacea to 

 notice. Some of the examples are of great rarity, and difficult to be ob- 

 tained, especially when entire and vigorous. 



I have not attempted to keep any order here, therefore this portion 

 of the work consists solely of miscellaneous observations. They are 

 merely notes, accompanying accurate delineations of living specimens. 

 The desultory form wherein what is said appears in this Volume entitles 

 it to no higher consideration than so many transient notes. 



Nevertheless, I feel confident that some utility will be derived from 

 the quality of the figures. The authors who professedly treat of Coucho- 

 logy, even the most experienced, are hardly yet agreed on the precise 

 position and arrangement of shells. Probably the subjects of their diffe- 

 rence will ultimately prove trifling : Possibly too much weight is given 

 to minutisB. It cannot be too often repeated, that the distinction of 

 animals and their parts should be very decided. Strongly marked, infi- 

 nite resemblances are general ; yet, on descending to the minutest fea- 

 tures, what two animals agree ? If two leaves from the same tree never 

 correspond, how can it be expected, amidst the variety of energies stimu- 

 lating the increment of living matter, that all the parts of two different 

 animals, such as may be visible or invisible to human sense, shall corre- 

 spond in otmiibus, — so great is the diflerence among the fingers of many 

 persons, that we could hardly credit they belong to the hands of the 

 individual ; and sometimes there is no likeness whatsoever between the 

 eyes. 



Differences of animals should be therefore very strongly imprmted ; 

 and when they are so imprinted, they may be chosen for prominent 

 features in distinguishing the genera and species which occupy the world. 



Neglect of this has undoubtedly led to considerable confusion in the 



