26 ON THE STUDY OF ZOOGEOGRAPHICAL REGIONS, 



suppose a species is recorded from Perth, Bunbury, Busselton, 

 Albany, Adelaide, Port Elliott, Murray River. In this case, we 

 might be justified in refusing to include the very barren coastal 

 region along the Great Bight within the contour, until we had 

 definite evidence of the occurrence there of the species in question. 



Suppose, then, that the contour of the group, planned on the 

 lines laid down, has been obtained. Of what value is it to usl 



i. It is a densiti/-contour for the group, but not an actual 

 species-contour. It takes account only of the number of species 

 occurring at a given point, not of the actual species comprising 

 that number. 



ii. It is not accurate in detail, but only in broad outline. 



If these two facts be continually borne in mind, the contour 

 may be used with very real value. The objects to be aimed at 

 in using such a contour are as follows : — 



1. To obtain on a single map a fairly accurate graphical repre- 

 sentation of the present distribution of a group. 



The author claims that the single " contour-map " will give to 

 the mind a clear and sufficiently accurate representation of the 

 distribution of the group, which cannot be attained by the perusal 

 of many separate maps, on each of which the area of distribution 

 of a single species of the group is mapped separately. 



2. By comparison of the Specific Contours of many groups over 

 the same region, these groups may be arranged into separate sets^ 

 each set possessing a contour referable to a single type, but not, 

 of course, similar in details. 



3. By a study of the different types obtained, the sum total of 

 the fauna or flora of the region may be clearly visualised, and its 

 different components clearly distinguished. 



4. In many cases, valuable phylogenetic evidence may be 

 deducible from a study of the contour. 



Before dealing more fully with these points, it is necessary to 

 consider (a) the general structure of a contour, (6) the general 

 theory of contour-types. 



