Rhynehart — Life-History and Bionomics of the Flax Flea-Beetle. 515 



margin. Exhibiting all the characters of a palp segment, it supports the 

 three-segmented maxillary palp. The basal segment of the latter is narrow, 

 strengthened by an enveloping band of chitin, and has on the inside (dorsal) 

 face one small bristle and two punctures. The second segment is similarly 

 strengthened, and has one small bristle on each of the dorsal and ventral 

 faces, and a couple of punctures dorsally. The terminal segment is sub- 

 conical, not chitinised, and does not carry any bristles. 



Labium (PI. XVIII, figs. 25 and 37). — This can easily be recognized by 

 the two short palps (/y).), which project ventrally and slightly forward. These 

 are simple, unsegmented structures, without any sensory appendages. They 

 arise from short, flat, ring-shaped palpifers (ffi^), which are supported on a 

 broad, rounded basal piece — the mentum (me.). Besides the palps, the 

 meutum carries a pair of long bristles, which are placed near the posterior 

 margin. It is supported by the globular and fleshy submentum {sm.), which 

 extends posteriorly to occupy the middle position as far as the gula. 1 1 has 

 two pairs of bristles, which arise near the lateral margins; one bristle at 

 each side is anterior, and the other is situated near the posterior angle at each 

 side. 



Anterior to the mentum and intimately fused with it is a well-defined area 

 provided with a number of minute but distinct structures. This is the 

 remarkably modified ligula (%.) or fused labial laciniae and galeae. The 

 structures which it bears are obviously sensory organs, and no doubt are 

 equivalent to the spines and bristles already described as occurring on the 

 apices of the maxillary laciniae and galeae. There are five of these organs 

 at each side of the middle line of the ligula. The two nearest the anterior 

 margin have strongly chitinised bases, from which project pointed spines. 

 Posterior to these are two pairs ; the inner pair resemble minute cylinders, 

 and are not provided with observable projecting spines, but the other (outer) 

 pair have pointed processes arising from circular pits. The next pair resemble 

 those last described, and the posterior pair are similar to those described as 

 the inner pair of the second anterior row. In young larvae the bristles of 

 these structures are usually longer than in fully grown larvae, while 

 occasionally an extra organ is present at one side or the other. Fig 13, 

 PI. XVIII, shows the general arrangement of these structures and of the 

 other parts of the labium. The tip of the hypopharynx is seen projecting 

 beyond the ligula. 



Hypopharynx (PI. XVIII, figs. 32 and 37). — This is closely attached to 

 the labium. In preparations of the complete head it is seen as a rounded 

 prominence, occupying the greater part of the region between the 

 mandibles immediately ventral to the opening into the buccal cavity. Under 



SCIKNT. PKOC. K.D.S., VOL. XVI., NO. XXXIX. 3 H 



