INTRODUCTION. 



In the present volume upwards of 2000 species of the family 

 Tenthredinidce are enumerated, and of the family Siricidce nearly 

 100. 



These insects have been much neglected by entomologists: in 

 Europe only and, to some extent, in North America have they been 

 assiduously collected, whilst our knowledge of the exotic forms is 

 very imperfect. No attempt therefore has been made to alter 

 materially the classification and arrangement of the genera generally 

 adopted, viz. that proposed by Norton in his Monograph of the North- 

 American Tenthredinidce and Uroceridce (Siricidce), in the ' Transac- 

 tions of the American Entomological Society/ vols. i. & ii. 



Parthenogenesis is very common in the Tenthredinidce, and the 

 females are generally far more abundant than the males : hence in 

 many species one sex only is known. The sexes do not usually 

 differ very much in coloration : those of Dielocerus ellisii and Ptenus 

 serratus are among the most dissimilar with which I am acquainted. 



The species do not appear to vary greatly. On the other hand, 

 the same distribution of colour and pattern not unfrequently 

 reappears in widely separated species, so that two specimens may 

 appear identical at first sight, whereas a closer inspection reveals 

 structural differences in their antennae and neuration, which prove 

 them to belong to widely separated genera, or perhaps even to 

 distinct subfamilies. 



