NO. 1310. NORTH AMERICAN THYSANOPTERA—IIINDK 108 



found in ^Eolothripidte can sometimes be observed in this family. 

 Ttie hind wings have always one longitudinal vein, but no ring or 

 cross veins. 



The wings of Phloeothripidte are marked })y the absence of veins. 

 In ])oth fore and hind wings alike there is but a partial development 

 of one median longitudinal vein. This is quite strong and marked at 

 the base, but rarely reaches to the middle of the wing before it disap- 

 pears. There is no trace of a ring vein, 



Fringimi. — As a rule, fringes of long, slender hairs are borne upon 

 both margins of the wing and so make up for the narrowness of the 

 membrane. The hind fringe is always present, but the fore fringe is 

 nearly absent in ^-Eolothripidw, always present in Phloeothripida?, and 

 more or less fully developed in Thripidge, The front fringe consists 

 of a single row of hairs which, when fully developed, are stouter in 

 Terebrantia than those upon the hind edge, but in Phheothripidfe they 

 are similarly developed on both edges. In some Thripidtxi the front 

 fringe is vestigial, being very weak and sparse, or it may be entire!}^ 

 absent. On the hind wings the front fringes are more uniformly well 

 developed than upon the fore wings, and both fringes are single. The 

 hind fringe of the fore wing in Terebrantia consists of two rows of 

 hairs so placed that they stand, when in flight, at diflerent angles to 

 the edge of the wing and thus by crossing give mutual support and 

 form a mesh-work which is more stronglj^ resistant to the air. The 

 hind fringe hairs of l)oth wings in Terebrantia are more or less wavy 

 or spiral in form while those of the front fringes are straight, as are 

 also both fringes in the Tubulifera. The hind fringes of both wings 

 of Tu])ulifera are single except that near the end of the fore wing the 

 fringe is double for a short distance. The length of the hind fringes 

 is from two to seven times the breadth in the middle of the wing. 

 Fringes are wanting near the base of the wings. 



The method of insertion of the fringes differs in the suborders and 

 is of interest. In the wings of Tubulifera the hairs are inserted 

 directly for some distance into the membrane of the wing, where they 

 graduallj' disappear. Thej^ are so flexible near the base that they can 

 be bent back along the edge when the wings are folded at rest. In 

 Terebrantia, however, the fringe hairs are borne upon small support- 

 ing bases on the edge of the wing and are in general stifler than are 

 those of Phloeothripidffi. One row of those upon the hind margin is 

 attached differently from the other. The hairs stand upon small, 

 conical, basal enlargements, to which the}^ are attached by a joint so as 

 to allow an easy folding of the long hairs toward the tip. Toward the 

 base of the wing, however, the side of the somewhat conical support is 

 drawn out into a point, which prevents the folding of the hairs toward 

 the base and keeps them at nearly right angles to the edge of the wing 

 during flight. 



