256 ME. "W. F. KLRBT— A EEVISION OP 



separating genera. It is generally more or less thickened at the base, and sometimes 

 inflated or gibbous; while towards the tip it is frequently widened and flattened. 

 These characters, though by no means confined to one sex, are sometimes more 

 pronounced in the male {Scapanea). 



The abdomen normally consists of ten segments. The first is a short basal segment, 

 and the second and third are usually thickened, and crossed by one transverse carina, 

 rarely more (only in Pantala). The fourth segment is also sometimes transversely 

 carinated, though the carina is frequently imperfect or merely indicated. Along the 

 dorsal line from about the carina on the third segment to the extremity and along the 

 sides run longitudinal carinae ; between them the abdomen either falls away from the 

 dorsal ridge, like the roof of a house, or is more or less rounded oflf; the under surface 

 of the body is generally quite flat in preserved specimens. 



Different as are Libellula sabina, Dru., and L. bnmnea, Fonsc, in the shape of the 

 abdomen, yet I am compelled to include them both for the present in the great genus 

 Orthetrum, Newm., which will take in all, or nearly all, the Old-World species usually 

 referred to Lepthemis, Hag. They represent the extremes of a long series of species 

 which lead us by insensible gradations from one to the other. The genus Trithemis 

 will also include a long series of species differing very considerably in the shape of the 

 abdomen, and most of which have been, in my opinion, less correctly referred by 

 previous authors to Biplax {=^Sympetrum) and Erythrodiplax. 



g. Abdominal Appendages. 



Although these are frequently of very striking forms, and cannot be passed over without 

 notice, yet it appears to me that their classificatory value in Neuroptera has been to 

 some extent overrated. In the Libellulinse their forms are frequently very similar ; and 

 I have only employed them as occasional accessory characters. It would be quite 

 conformable to all analogy for these characters to be of paramount importance in one 

 family, and of little or no value in another. In Coleoptera, for instance, Dr. Leuthner 

 states' that the structure of the male sexual organs is important in the Dorcidee, but 

 useless for classification in the Lucanidee. Besides, wherever possible, it is desirable to 

 avoid laying too much stress on characters which are peculiar to one sex. 



Appendages of the Second Segment of the Abdomen. — The true organs of generation in 

 the male are placed beneath the second segment; they generally present the appearance 

 of two distinct prominences, between which is a longer and more slender projection, 

 often double, with a hook at the extremity directed backwards. This is known as the 

 hamulus, and differs considerably in structure in different species. The appendages of 

 the second segment are more or less prominent ; and in the genus Misagria they are 

 simply enormous, nearly equalling the thickened base of the abdomen itself in bulk. 



Appendages of the Eighth Segment of the Abdomen. — These are found in the female 

 ' Trans. Zool. iSoo. vol. xi. p. 393. 



