INTRODUCTION. 



15 



7. Infect reddish-brown, with black patches on the pronotum. Sp. no. 7. 

 Insect lighter brown, with no black patches on the pro- 

 notum Sp. no. 8. 



(3) The double numerical form. 



1 (8) Anterior coxal cavities open behind. 



2 (5) Antennae passing beyond the base of the pronotum. 



3 (4) Pronotum black, elytra yellow Sp. no. 1. 



4 (3) Pronotum and elytra brown Sp. no. 2. 



5 (2) Antenna) not passing beyond the base of the pro- 



notum. 



(7) Insect blue, with purple stripes on the elytra Sp. no. 3. 



7 (6) Insect with no such stripes on the elytra Sp. uo. 4. 



8 (1) Anterior coxal cavites closed behind. 

 9(12) Eyes emarginate on the inner side. 



10 (11) Insect elongate, parallel-sided, with the upper side 



black and underside yellow Sp. no. 5. 



11 (10) Insect with no such combination of characters # . . . . Sp. no. (5. 



12 (9) Eyes not emarginate on the inner side. 



13 (14) Insect reddish-brown, with black patches on the pro- 



notum Sp. no. 7. 



14 (13) Insect lighter brown, with no black patches on the 



pronotum Sp. no. 8. 



In the foregoing three imaginary keys the same characters have 

 been used in three different ways. It will be observed that 

 essentially keys no. 1 and no. 3 are the same, the categories being 

 stated in the same order. In key no. 1 the arrangement of the 

 categories depends upon the space, they being gradually shifted 

 from the left to the right. This becomes a disadvantage when a 

 large number of forms is dealt with. Key no. 3 overcomes 

 this difficulty by numbering them as shown, e.g. 1 (8) means that 

 the character contradictory to that stated under 1 should be looked 

 for under 8 and vice versa. The principle involved in key no. 2 

 is different ; the contradictory categories are stated at once, one 

 immediately following the other, and numerals are placed on the 

 right-hand side indicating where the further divisional categories 

 are to be looked for. An important point is that all forms fol- 

 lowing the statement of a character must possess that character 

 in common: for example, in key no, 2, all forms from 1 to 4 

 (Inclusive) possess the character stated under 1, and those after 

 5 possess the contradictory character ; in key no. 3 all forms 

 from 1 to 7 (inclusive) of the first row of numerals possess the 

 character stated under 1 in common, and those after 8 possess 

 the contradictory character ; while in the spatial arrangement 

 this principle is obvious. In key no. 2 numerals are found on the 

 right as well as on the left margin ; in no. 3 the numerals are 

 placed on one side, and the cross-references are indicated by 

 numerals in brackets running in a parallel column. 



