LOCUSTODEA. 149 



between the swollen bases of the lono^ antennae to a 



o 



greater or less extent, and in various forms. The 

 margin of the vertex is separated from the frons by a 

 furrow, immediately below which is the vestige of the 

 median ocellus, the lateral ones being absent. 



Of the pronotum the lateral ridges are usually 

 wanting (but maybe seen in one or two of our species), 

 and the median one, if present, is not strongly marked.. 

 In some cases the side flap runs backwards in a single 

 curve, but in others it is hollowed out at the shoulder. 

 The prosternurn may be plain or armed with two spines. 



Normally the venation of the elytra is somewhat 

 simple, there being the subcostal nervure, the radius,. 

 medius, and cubitus, followed by the first anal nervure, 



e/ 



the dividing nervure, and the remaining anal nervures; 

 the anal area beyond the dividing nervure is in the 

 male modified to form a musical apparatus. In this 

 region the left elytron, which at rest overlaps the 

 right, has the nervures thickened, especially below;. 

 while in the same part of the right elytron is a bright 

 transparent "speculum ' -a vibrating membrane. The 

 rubbing together of the two elytra produces the 

 " song," a kind of file on the left elytron passing 

 across a sharp edge on the right one, and the whole 

 forming a sort of violin. These musical organs are 

 found in the male only, except in two non-British 

 families. In species in which the elytra are greatly 

 reduced, it is these parts which remain. The tympana 

 or " ears'' are on the tibiae of the forelegs. The 



o 



'song' is more shrill than in the next group, the 

 Acridiodea, in which, too, the sound is produced in a 

 different manner. 



Though the British species are easily distinguished 

 without their aid, the number and position (or the 

 absence) of spines on the tibiae are used in classifica- 

 tion, while the presence or absence of apical spurs is 

 important for the same reason. As already mentioned 

 the fore tibiae of the male bear near their base the 

 tympana, or external " ears," which may be oval, 



