184 Memoirs of the Indian Museum. [Voi.. Ill, 



found in the first section. These extend obliquely forwards and outwards from 

 the front of the central tubercle. Close to their origin they are in some species 

 more or less fused, to form a short median keel. The extent of this fusion, as 

 well as the precise course followed by the ridges, has been found to vary greatly in 

 different specimens of a single species (see, for examples, fig. 19, and figs 52 and 

 52&, c and d). In spite of the great differences in the general appearance of an 

 insect produced by these variations, they have rarely been found to have any 

 taxonomic value at all ; and in these rare instances they have always been found in 

 association with more distinctive, though perhaps less striking, characteristics in other 

 parts of the body. 



In some forms the frontal ridges are replaced, or defined on the anterior and 

 inner side, by a fine groove which extends almost up to the tubercles in which the 

 ridges normally end, a little behind which it either disappears or bends outwards and 

 a little backwards (see, for examples, figs. 25-39 inclusive). Another groove (which, 

 though easily seen in most specimens of Aulacocyclinae, is more obscure in the other 

 subfamilies, especially after the insect has become hard and black) extends backwards 

 on each side of the head from the anterior margin close to the inner side of the supra- 

 orbital ridge, and curves inwards as though to meet the former groove, when it too 

 disappears. There is usually an abrupt bend in the course of each frontal ridge 

 opposite the place where the lateral grooves disappear even in species in which no trace 

 of a frontal groove is visible. Consequently there can, I think, be little doubt 

 that the lateral grooves, and those which sometimes follow the course of the 

 posterior parts of the frontal ridges, together represent the suture by which the frons 

 is separated from the parts of the head that lie on either side of and behind it ; and 

 that the posterior parts of the frontal ridges always follow the course of this suture 

 even when the suture itself is no longer developed.' 



The course of the division between the frons and the clypeus, or plate imme- 

 diately in front of it morphologically, is less evident, and it will be convenient to 

 describe the characters of taxonomic interest in the two plates together before going 

 on to enquire into this. 



The pair of tubercles in which the frontal ridges end may be called the inner 

 tubercles, as they are always found either on the folded anterior margin of the head 

 between a second pair of tubercles, the outer tubercles, or else behind these away from 

 the margin. That the inner tubercles are morphologically the same, no matter which 

 of these positions they occupy, becomes evident as soon as the lower surface of the 

 folded anterior margin of the head is examined.^ 



' In pupae there is often a deep groove running direct from the position of the lateral grooves to the 

 angle between the central tubercle and parietal ridges of the imago; but this appears to me to be 

 no more than a fold in the pupal skin caused by the broad depression beneath it. Even if this fold should 

 prove to appear, in the first instance, along the line of the sutures that bound the frons in the larva, it 

 would not necessarily prove the above conclusion incorrect, as the plates which develop beneath it may 

 well be of a different shape from those which they replace. 



'^ Before this can be done the whole of the labrum must be removed. 



