THE BIOLOGY OF THE ALDER FLEA-BEETLE. 259 



to form the prothoracic and anal shields respectively ; one pair 

 of jointed legs borne by each of the thoracic segments; a single 

 median anal proleg borne by the 10th abdominal segment. 

 Length 1 cm. 



Head directed obliquely downward and forward ; strongly chitinized, 

 shining black; the epicranial suture, at first extending cephalad along the 

 mesal line, soon splits, passing back of the antenna to the base of the 

 mandible on each side; it divides the head into three large segments, 

 the median dorsal one the postclypeus, and the other two forming the 

 epicranium; the clypeus is very narrow; labrum moderately large, rounded 

 in front, shining black ; mandible dark brown, moderate in size, with 

 notched teeth at the apex; trochantin present at its base, non-chitinized ; 

 ma.villa, with the cardo completely, the stipes incompletely, chitinized, 

 bearing anteriorly a palifer with a 3-segmented conical palpus, and a 

 very small nodule which probably represents the lacinia; labium with 

 a large slightly chitinized basal piece, the fused mentum and submentum, 

 bearing a ligula, unchitinized except at its base, from which arise a pair 

 of small 2-segmented palpi; antennae inserted on the side of the head 

 near the base of the mandibles, 3-jointed, white, the basal segment much 

 larger than the middle segment, and the distal segment very small; 

 ocelli wanting, the large sclerite between the labium and the prothorax 

 (figure 18 B and C) is the gula. 



Body wall of thoracic and abdominal segments brownish, densely 

 beset with dull black cuticular nodules ; prominent dull black dorsal, 

 dorso-lateral, and lateral tubercles; ventro-lateral and ventral tubercles 

 dull brown. 



Abdominal segments i to 8 bear setiferous tubercles, segments 1 

 through 7 being identical; on the first 7, the setae are arranged in a mid- 

 dorsal row of 2 tubercles on each segment (the anterior the larger), an 

 upper and a lower row of dorso-lateral tubercles above the spiracle (each 

 row composed of 2 small tubercles on each segment), a lateral row of 

 prominent tubercles just below the spiracle (one tubercle to each seg- 

 ment), an upper and a lower row of ventro-lateral tubercles (a single 

 tubercle each, on each segment), and a median ventral row (a single 

 tubercle on each segment) ; on the 8th, the arrangement of the tubercles 

 is the same except that the posterior of the mid-dorsals is the larger, 

 and the upper and lower posterior dorso-lateral tubercles have united 

 into a single one. 



Abdominal segment 9 is modified dorsally into a strongly chitinized 

 anal shield ; ventrally it bears a large median tubercle, not clearly homolo- 

 gous with the other abdominal tubercles. 



Abdominal segment 10 is very small; it has no setae nor tubercles, 

 but bears ventrally the orange-yellow anal proleg (which probably repre- 

 sents the fusion of a pair of prolegs) ; the anal opening is shaped like 

 an inverted Y, and lies in the middle of the proleg. 



Metathorax and mesothorax. Mid-dorsal tubercles are present, homol- 

 ogous with those of the abdominal segments; they are broken along the 

 mesal line (to provide a thin place where the cuticula can yield to strain, 



