6 THE FAUNA OF SCOTLAND. 



when we bear in mind that Poecilosoma contains species that have 

 only three marginal cellules, and no medial cellule in the posterior 

 wing, this can scarcely be regarded as a serious objection against 

 uniting these genera into a sub-tribe. In the form of the lanceolate 

 cellule, they all coincide more or less, there being a nervure 

 (generally oblique) in all of them except Strongylogaster. I am 

 not sure, however, but that the proper position of the last named 

 genus may be among the Selandriades. 



The Dolerides are most nearly related to Tenthredo, and have 

 no relationship with Emj^hytus, near which they are placed by 

 the German authors. I place them between Allantus and 

 Strongylogaster, as perhaps the best position, but they are very 

 distinct from any of the other sub-tribes. In seeking to place 

 such anomalous tribes in a series in our Catalogues, we must bear 

 in mind that a natural classification is one which represents the 

 different forms branching out in various directions from a common 

 stem, and that of the once numerous branches we only now know a 

 few disjointed twigs — not one which shows them in a straight row. 



A word or two may also be said regarding the formation of the 

 genera in this family. For my own part, I consider that if any 

 group is distinct enough to have a name attached to it, it should 

 be called a genus ; sub-genera I consider to be more apt to lead 

 to confusion than anything else. In this respect, the named sub- 

 suh-suh-siih -sections of Hartig are cases in point. No doubt if the 

 above view is followed it may lead to mere artificial sections 

 being formed into genera, but I hold that, in the present state of 

 the Hymenoptera, this is a less evil than to have large genera 

 containing a number of well marked sections. Take, for example, 

 the loose way in which the terms " Selandria " and " Allantus " 

 are used. I could point out numerous descriptions of new species 

 described under these names where there is nothing to show in 

 what limit the genus is defined; i.e.y whether the species is a 

 Selandria in the restricted sense, or a Blennocampa, or perhaps it 

 may be a Poecilosoma. And this loose definition is especially 

 troublesome in investigating foreign insects. 



The parts most useful in defining genera are (a) the antennae ; 

 the number and position of the joints, (when the number exceeds 

 9 they are variable, and consequently mere number then is not 

 of much use); their covering; and the relative lengths of the joints ; 

 (h) the neuration of the wings, more especially the number of 



