67 
broader behind than in front; it can be retracted into the cephalo- 
thorax just below the dorsal surface. This plate is divided by a median 
line or sulcus; on each side below and toward the tip there arises a 
long and slender curved stylet. This plate appears to be formed 
by the union and flattening of the basal joints of the mandibles. 
Fie. 2.— Tetranychus: mandibular plate, dorsal and lateral views: a, plate; b, stylet; ¢c, spina; d, 
palpus—highly magnified (original). 
Below this plate is a rather large and conical rostrum, from each side of 
the base of which arises a palpus, each composed of five joints. The 
penultimate joint ends in a large claw; the last or **thumb” projects 
little if any beyond this claw, and bears one or more projections or 
“fingers” on its tip or sides. In some species, perhaps all, the palpus 
of the male has a short, 
curved spine on the tip of 
the upper side of the third 
joint. The rostrum at tip 
has a cylindrical projec- 
tion, rather enlarged at 
the end, consisting of a 
piece each side, which is 
possibly the maxilla. The 
opening between the two 
is the mouth. At the tip 
of the abdomen on the FG, 3.—Tetranychus: cephalothorax from above: a, palpus; 
ventral surface is the anal b, mandibular plate ; ¢, frontal bristle ; d, subfrontal bristle; 
z e, eyes—highly magnified (original). 
opening, often showing ‘ 
from above at the tip of a median pointed projection. On the venter 
slightly in front of the anal orifice is the genital opening. In the 
female it is surrounded with variously curved striz; in the male it 
is much less conspicuous 
a simple slit inclosing a rather slender 
curved penis. The vulva in the various forms appears somewhat 
different, although on the same plan. But the difficulty of examin- 
