CARD CATALOGUES AND THEIR APPLICATIONS. 101 
In sorting the cards into their places by the numbers, 
the first will find its way to Tertiary period; the second to 
Australia, Victoria; the third to appendages of the body- 
fixing organs ; and the fourth to bryozoa, gymnoleemata, genus 
Adeona. Thus it will be seen that the information it contains 
will be supplied to the seeker from whatever avenue he may 
approach it. 
This facility for double and multiple reference is perhaps 
the most striking feature of Dr Field’s system. 
The rule which applies to the arrangement of books in 
a library—classify every title in the most minute division 
possible—is of paramount importance in a work like the 
present, where it is so necessary to restrict the number of 
cards to be examined by any one in search of definite infor- 
mation. The need for subdivision is seen when we consider 
such a group as the butterflies, a favourite object of study by 
naturalists, both professional and amateur, in all quarters of 
the globe, on which as many as 1200 works have been 
published in a single year. To meet such cases a special 
method of classification has been devised. The limits and 
number, and even the very names of families, are by no means 
agreed upon among naturalists, hence it is out of the question 
to carry out the decimal scheme to groups of such small 
systematic value. An alphabetical arrangement has therefore 
been adopted in the case of papers dealing with a single 
family or genus, the name being affixed to the class number 
in order to serve as a guide to placing the cards in sequence 
(see Example 3). 
In order to facilitate reference, the catalogue is provided 
with guide cards such as are familiar to every one who has 
worked with a card catalogue. Dr Field has published a 
series of these guides, of graduated sizes, with a tab project- 
ing above the level of the cards, and having on it the name 
of the main division, so that this at once catches the eye. 
Each main card, too, bears a printed list of its subdivisions 
with their numbers. 
