XVIU INTRODUCTION. 



The mentum articulates with the anterior margin of the gula, 

 which is sometimes prolonged forming a peduncle; the suture 

 separating them is called the mental suture. The openings on 

 each side of the mentum are called the buccal fissures; these 

 permit free motion of the basal pieces of the maxillae. 



The mentum varies greatly in form and size, and gives im- 

 portant characters in the system of classification. It is usually 

 small or moderate in size, trapezoidal or quadrate ; rarely it is so 

 large "as to completely close the mouth beneath ; it is frequently, 

 as in CarabidiB and allied families, deeply emarginate in front, 

 with a prominence called a tooth at the middle of the emargina- 

 tion; the presence aud form of this tooth are of generic value. 

 When deeply emarginate the lateral portions of the mentum are 

 called the lobes; these are bordered on the inner side by a narrow 

 piece, somewhat inflexed, extending even to the bottom of the 

 emargination, and contributing to the formation of the tooth; 

 these are called the epilobes of the mentum. Their structure 

 has been used by Chaudoir for the definition of genera of Cara- 

 bidae, but no use is made of them in the present treatise. 



In many families, especially in the Clavicorn and Serricorn 

 series, the mentum appears to be divided into two portions; this 

 results from a piece between the mentum and labium, called the 

 bypoglollis, and which is usually entirely concealed, coming into 

 view by reason of increased development; in the Carabidce the 

 homologous portion is often called the " basal membrane of the 

 ligula," and is sometimes sufficiently developed to fill the emargi- 

 nation of the mentum. 



The labium is placed usually in front of the mentum, or in the 

 emargination between the two lobes ; rarely it is almost entirely 

 concealed. Three members enter into the formation of the labium 

 — a central piece called the ligula, and on each side the para- 

 glossse; often the labium is entirely corneous, in which case the 

 paraglossae may be completely united with the ligula or even 

 absent. The ligula is usually corneous, at least in part, often 

 membranous ; its form and size vary greatly. The paraglossge 

 are usually membranous; ihey reach their fullest development in 

 the Carabidte, and their variations have been used in classifica- 

 tion. As the paraglossae are often entirely absent, and the ligula 

 alone remains, the term ligula has come to be used synonymously 

 with labium. 



