^08 



ON THE GENUS PETALURA, AVITH DESCRIPTION 

 OF A NEW SPECIES. 



By R. J. TiLLYARD, M.A., F.E.S. 



(Plate xxxiii.) 



The genus Petalura was created by Leach in 1815 to contain 

 a remarkable dragonfly of great size which he received from his 

 friend, W. J. Hooker, from "New Holland" (N.S.W.). The 

 insect was absolutely unlike an}^ other dragonfly known to Leach, 

 but he placed it in the family uEschnidte, although he was careful 

 to remark upon the many diff'erences it possessed from all other 

 members of that family. Since then it has remained for a long 

 time classed with the subfamily Gomphince, until only lately 

 Kriiger has removed it and constituted a new family, Fetaluridce, 

 to contain it, placing it between Gomphince and the Calo^^terygidce. 



Before we attempt to place the genus arbitrarily in any assigned 

 position, we must recognise the difficulty that always occurs in 

 dealing with aberrant genera. It is this. All naturalists admit 

 the imperfections of a simply linear classification, in which an 

 attempt is made to arrange in a definite line a series of genera or 

 families on which the forces of natural selection have been 

 exerting themselves through countless ages. That it can be done 

 at all shews us indeed that all natural development has proceeded 

 more or less on the same lines; and that if Nature is prodigal in 

 variation, she is nevertheless chary in innovation. But it some- 

 times happens that a whole race, or a series of races, has been 

 completely wiped out in the past, save, perhaps, for some solitary 

 form, more stable that its congenei-s. Such a form, or forms, on 



