Xxii INTRODUCTION. 



forming a single piece; the suture which separates the meso- 

 sternal and metasternal side pieces from each other is always 

 distinct. The form and extent of these side pieces are of great 

 importance in classification, and characters drawn from them have 

 been found very useful in a large number of families. 



In the Carabidaj and some other families the metasternum is 

 divided into two unequal portions by a suture which runs trans- 

 versely a short distance in front of the posterior border ; the 

 smaller piece which borders the posterior coxiB in front and 

 often passes between them, meeting the abdomen, is called the 

 ante-coxal piece of the metasternum; its presence and extent 

 determine the division of the Adephagous series into families. 



These sternal side pieces are often called collectively the jmra- 

 pleurse of the respective segments. 



Wings. — The anterior or mesothoracic pair of wings in Cole- 

 optera are horny plates, called elytra, and vary greatly in shape 

 and s(Hilpture ; faint traces of nervures are seen in many families 

 in three or four lines of different sculpture ; they usually cover 

 the dorsal surface of the abdomen, but in many genera of widely 

 differing families are very much shorter. The sides of the elytra 

 are often limited by an acute margin, beneath which a portion of 

 the elytron is inflexed; bordering the inner edge of this inflexed 

 portion is a piece of varying width, extending sometimes from the 

 base to the apex, called epipleura. The entire inflexed portion 

 is sometimes erroneously called epipleura; in the present treatise 

 the term is limited as above defined. The elytra are sometimes 

 entirely wanting; this, however, is very rare in our fauna, and 

 confined to a few females of some genera of Lam|)yrida3. 



The posterior or metathoracic pair of wings are membranous, 

 and have but few nerves; these are so arranged in most instances 

 as to form a joint near the extremity, whereby the wing can 

 be folded entirely under the elytra ; in some genera with short 

 elytra the wings are extended straight along the dorsal surface 

 of the abdomen. The venation is subject to variation, but no 

 results of importance for classification have yet been obtained 

 by a study of these organs. Frequently the wings are entirely 

 wanting, in which case the metasternum is usually short, and the 

 elytra closely united or connate. 



