TROMBIDIIDAE OF MINNESOTA WZ 
and other vegetable matter in low bottom lands along the Minnesota 
River near Minneapolis, also under decaying leaves in woodland about 
Lake Minnetonka and near the University Farm Campus in May 1917. 
Ewing records this species as collected from under the bark of an 
ash tree. In the laboratory we were unable to ascertain anything as 
to its habits except that it seems to prefer wet, decaying vegetable 
matter as its habitat. It is the smallest of our local trombidiums. 
Microtrombidium triangulum, n.sp. 
Adult female. Color, dark scarlet, lighter when engorged. 
Body elongate oval, broadest in front, narrower behind where it is 
broadly rounded, no marked median constriction. Size—1.55 mm 
long by 1 mm wide. Dorsal surface with a shallow transverse groove 
posterior to the cephalothorax, two other strongly marked transverse 
grooves, and at the posterior end three pits in the form of an inverted 
triangle, these and the tips of the grooves are connected by longitudinal 
grooves. On the ventral side a transverse groove posterior to cephalo- 
thorax and another below coxae I and II; genital opening opposite 
coxae IV; anus just posterior to genital opening. Surface of body 
covered with short, stout, spindle-shaped hairs, each covered with 
numerous branches. In the region of the cephalothorax and in the 
median portion of the venter these become long and more slender. 
The hairs on the legs are slender and branched. 
Cephalothorax entirely exposed, wider than long. Eyes sessile, 
Dorsal groove with a prominent posterior expansion, Palpi short and 
stout, segment II swollen, two thirds as wide as long, segment III, as 
wide as long, a third as long as II, segment IV longer than III, two 
stout claws, the inner smaller thumb short and thick, pointed at tip, on 
the outer surface of segment IV a row of stout bristles forming a crest 
on the dorsal margin, seven other bristles arranged in diagonal rows on 
the outer face. The inner surface bears one heavy spine at the base of 
the thumb. 
Legs slender, lighter colored than body, Tarsi I, short and swollen, 
a little less than half as wide as long. 
Male. Similar to female—length 1 mm long by 0.70 mm wide. 
Larva, unengorged. Of a light yellowish orange color. Body 
slender, length 0.25 mm by 0.13 mm wide. On the anterior end the 
chitinous shield is an elongate pentagon, not quite twice as long as 
wide, the two anterior edges are curled in toward the ventral side, a 
pair of small spines near the rounded anterior end and another near 
each posterior angle, in a large pit. Eyes are triangular plates laterad 
of the shield. Posterior shield quadrilateral, short and a little wider 
