78 BRITISH APHIDES. 



Europe, except the extreme north, penetrating along 

 the chain of the Caucasus a considerable way into 

 Central Asia, they seem only to occur in America 

 through an artificial introduction. Probably the iso- 

 lating action of the two great oceans which wash the 

 shores of this continent has prevented the migration of 

 these fragile insects. Numerous Aphides, however, 

 there occur on the Oaks peculiar to the States of 

 America. 



Before concluding . these remarks, I will notice an 

 Aphis which Mr. Walker preserved in Canada balsam, 

 and afterwards presented to me. He named it Jj^/iis 

 cistata, but I believe he never described it. 



The winged form is the only one I have seen, and 

 therefore I cannot furnish figures. The insect has 

 many of the characters of Dryobius. 



Dryobius cistatus, Walk. 



Inch. Millimetres. 



Expanse of wings 0-380 9'64 



Size of body O'lSOx 0*040 3%30xl-01 



Length of antennse 0*050 1'27 



Thorax broad ; abdomen large and oval ; cornicles 

 inconspicuous. Head rather small ; antennee short, 

 the third joint the longest, the three following joints 

 about equal. Legs and wings rather short. Cubitus 

 stout, ending in a large clouded stigma ; cubital vein 

 very slender, the first furcation very fine, and the 

 second very difiicult to distinguish. Tlie first and 

 second oblique veins very thick ; the membrane 

 across these veins is slightly clouded with brown. 



Taken at Southgate, late in June, on the Spruce-fir. 

 The insect is not to be confounded with Aphis costata, 

 Walk., which would appear to be a Callipterus. 



