220 
IOWA ACADEMY OP SCIENCES. 
order named; the third nearly as longf as the sixth; apical joints subequal, 
minute; all joints thinly covered with microscopic hairs; bristles or stiff 
hairs on basal and intermediate joints which on distal joints are replaced 
by slender hairs; sensorial spines on the third, fourth and sixth joints, dis- 
tinct; clypeal, subantennal and postocular bristles present, the last less 
conspicuous than in tritici; mouth parts distinctly asymmetrical; each joint 
of maxillary palpi cylindrical, narrower than the preceding; first and third 
subequal in length, and second shorter than either. 
Prothorax about one and one-half times as broad and equally as long as 
preceding segment; anterior angles rectangular, posterior rounded, sides 
slightly converging cephalad; disc striate and sparsely hairy; front and 
hind borders more deeply striate or rugose, bristly; the most conspicuous 
bristles are arranged as follows: One long bristle at each anterior and two 
at each posterior angle; two shorter bristles on anterior margin, two on 
posterior margin and one on disc near each posterior angle. 
Meso-metathorax, subquadrate; mesoscutum more finely striate than 
prothorax, with small bristles, one at each lateral angle, two near and two 
on posterior margin; scutellum as long as mesoscutum, narrow, not strongly 
carinate; base transversely striate, sides longitudinally rugose; basal 
bristles as in tritici. 
Abdomen broad, ovate, basal segments and sides sculptured, bristles 
similar to those of tritici. 
Legs, with numerous short bristles; all tibiae and joints of posterior 
tarsi with terminal spines; anterior femora incrassate, their tibiae stout. 
Wings rather broad; humeral arch not prominent; surface minutely 
pilose; veins distinct, uniformly and heavily spinose; anterior and poste- 
rior basal cross veins present; cubitus inserted in marginal at tip of wing; 
radius obsolete at proximal end, but perceptible before it unites with the 
posterior basal cross vein; costal spines longer than those on the other 
veins, numbering from twenty-five to twenty-nine; cubital, from nineteen 
to twenty-three; radial, from fifteen to sixteen; anal, fi\re, gradually 
increasing in size from one to five; internal, one; posterior wings hyaline; 
longitudinal vein indistinct, except at base. 
This form approaches closely the dark colored specimens of tritici, from 
which it may be separated by its larger size, the annulus on the antennae, 
and especially by the shape of the head, which is pentagonal instead of 
rectangular, and the less approximate antennse- 
Described from twenty-nine specimens taken at Ames, Iowa, in July, 
August, September and January. 
Thrips variabilis n. sp. 
Head transverse Antennae eight-jointed, distant; ocelli approximate. 
Each posterior angle of prothorax provided with a single medium sized 
bristle; bristles on penultimate segment of abdomen not strongly radiat- 
ing, not extending backward beyond the base of the succeeding row; radial ; 
vein bispinose, obsolete; legs slender. | 
Female. Length from .84-1.23 mm. Head one-half as long as ' 
broad; viewed from above, subrectangular; anterior margin straight; occi- | 
put short, transversely convex and striate; distinct oblique depression 
behind each eye; genae moderately full; vertex abruptly ascending, tumid | 
