80 BRITISH APHIDES. 



the roots of Hioracium, to which he gave the name 

 Bhizobiu8 subterraneus. Signor Passerini, for conve- 

 nience, has adapted its characters for a sectional group, 

 and I here follow the lead of so good a naturalist. 



No winged forms have yet been discovered in this 

 group. Thus we lose the valuable help which would 

 have been afforded by a study of the wing-veining and 

 other characters attending a metamorphosis into the 

 imago. Again, the simplicity of the tarsal joints, and 

 the little light thrown on the matter by any reliable 

 variation in the mouth parts, and the want of all fixed 

 banding of pigment or colour on the bodies, render it 

 very difficult authoritatively to decide what should be 

 the points of a diagnosis. 



As an illustration of the variability of a genus I 

 cannot do better than quote Passerini's words, which, 

 though they apply particularly to the description of a 

 single insect, Bhizobius menthce, yet equally well suit 

 all the English species of this tribe. 



With reference to the antennal joints, he says, 

 11 Secundum astatem antennarum articuli numero vari- 

 ant. In junioribus articuli tres tantum extant, quorum 

 extremus caateris valde longior. Orescente state hie 

 apico dividitur, unde antennas quadri-articulatae fiunt; 

 et deinde articulus tertius, omnium sua vice longior, 

 apicem versus bis dividitur donee antennae sexarti- 

 culataa evadunt, articulis subaequalibus." 



Notwithstanding these undefined characters, consi- 

 derable interest attaches to the group on account of the 

 peculiar economy shown by its members. When the 

 insects are regarded as a whole, they certainly show to 

 the eye a peculiar aspect, which separates them from 

 all the genera previously described. 



One of the notable life-peculiarities concerns their 

 relations to ants. With few exceptions, all the species 

 are denizens of ant-hills ; and it is singular how insects 

 of such diverse habits and conformation can live and 

 thrive together. 



Many isolated observations have been made with 



