XIV INTRODUCTION. 



iug to the family ; rarely it is so large as to close over the buccal 

 openings, and thus conceal the base of the maxillae ; it is fre- 

 quently, as in Carabidse and allied families, deeply emarginate 

 ia front, with a prominence called a tooth at the middle of the 

 emargination ; the presence and form of this tooth are of generic 

 value. In many families, especially those with antennae of the 

 clavate and serrate types, the mentum appears to be divided into 

 two portions ; this results from a piece between the mentum and 

 ligula, called the hypoglottis, and which is usually entirely con- 

 cealed, coming into view by reason of increased development. 



The ligula is either corneous or membranous, usually oblong, 

 pointed, rounded,* or emarginate, or even cleft and lobed at the 

 anterior extremity ; usually prominent, rarely concealed behind 

 the mentum ; near the tip is usually seen on each side a mem- 

 branous process ; these are called paraglossae, but are frequently 

 wanting. Between the body of the ligula and the mentum are 

 the supports of the labial palpi ; these sometimes are largely 

 developed, and in certain Scarabasidae are entirely united together, 

 forming what appears to be the ligula ; the genuine ligula in these 

 cases is almost atrophied, and is concealed behind the corneous 

 plate formed by the labial supports. In the following pages the 

 term ligula is used in both cases, and is to be understood to mean 

 the piece in front of the mentum bearing the palpi, whether it be 

 the ligula proper or some other part. 



The labial palpi are usually 3-jointed, but occasionally 2-jointed 

 or even (certain Staphylinidae) filamentous, and not divided into 

 joints. In the genus Aleochara they become 4-jointed, by. the 

 addition 'of a very minute terminal joint. They vary in form. 



THORAX. 



The second division of the body is called the thorax, and con- 

 sists of three segments which support legs, and which are variously 

 modified as regards size and union in the different orders of 

 insects. 



In Coleoptera the first of these segments, the prothorax, is 

 separate from the other two, and is freely movable ; it consists of 

 a dorsal surface, the pronotum, consisting normally of four pieces, 

 which in Coleoptera are never distinct; two pairs of pieces form- 



