16 INTRODUCTION, 
I do not wish to find fault with the men who described and 
figured shells; it is the determined pertinacity with which the 
species-maker adheres to and insists upon the characters being per- 
manent with which I disagree. Naturalists in the early days of 
Conchology had few if any opportunities of judging how far the 
system of making shells distinct might be correct ; in fact it is only 
within the last few years that we have been enabled to obtain the 
necessary materials for comparison, 
With specimens most of which were rare and consequently 
high in price, even the rich were content with obtaining one or two 
examples of each. Of late years the influx of shells has produced 
the desired effect of rendering them easily procurable and at mode- 
rate prices, so that a few more or less is not now considered to be 
of much importance to the purchaser. The study of any particular 
division of this subject may be carried on for years by persons of 
moderate means, and materials may now be obtained to prosecute 
any line of investigation with comparative certainty of being able 
to pursue it with success. 
The more extensive the subject of Natural History becomes the 
greater will be the necessity for men to confine their studies to 
separate branches of the science. By limiting our study to a single 
generic or even sub-generic division we can find ample means to 
examine the subject in all its details. Scientific men are and have 
been turning their attention more to the extension of knowledge in 
the form in which it is here carried out than in trying to grasp at 
more than the understanding is capable of retaining. Any of the 
divisions of the smaller Trochi, such as Euchelus, Ziziphinus, 
Trochocochlea, Omphalius, or that charming little group of shells 
Clanculus, might be examined with a certainty of obtaining very 
satisfactory conclusions. 
The Mitres present characters very similar to those in the 
genus Nassa, and might be studied with every probability of 
interesting results. 
