Rhynehakt — Life- History and Bionomics of the Flax Flea-Beetle. 511 



The average length is 0-59 mm. aud the average greatest breadth 0-23 mm. 

 The size is, however, not uniform, as the following measurements of eggs from 

 different clusters show : — 



Length Greatest Breadth 



(mm.) (mm.) 



0-55 0-17 



0-61 0-23 



0-61 0-28 



0-6i 0-29 



0-55 0-20 



0-58 0-21 



(5) The fidly grown Larva (PI. XVII, fig. 23).— The details of the larval 

 descriptions which follow are from fully grown specimens, and to avoid 

 repetition the description of the fully grown larva is placed before those of 

 the earlier stages. 



The length varies from 3'6 mm. to 4-5 mm., according to the time that 

 had elapsed since the previous moult. Form narrowly elongate, nearly 

 cylindrical, the sides more or less parallel from the posterior margin of the 

 prothorax to the posterior margin of the eighth abdominal segment, the 

 average diameter being 0'40 mm. Colour opaque white, excepting for the 

 head and the posterior end of the abdomen (ninth abdominal tergum), which 

 are firmly chitinised and of a dark orange-yellow colour. The cuticle otherwise 

 is soft throughout, and bears numerous brown coloured bristles on indistinct 

 tubercles, which are placed on the body in a regular order. 



(i) Head (PI. XVIII, tigs. 25, 26, 27).— This consists of a strongly 

 chitinised capsule, which completely envelops the dorsal and lateral regions. 

 Veutrally, the head is feebly chitinised and white in colour. The chitinous 

 part is dark yellow or orange, and when viewed from above with a low- 

 power binocular is seen to be divided into two distinct parts by a narrow 

 dark ridge, which extends along the median line. The capsule is strongly 

 arched towards the posterior margin, and the latter is hollowed out into a 

 deep V-shaped groove. From the centre of the groove the epicranial suture 

 (epsu) extends anteriorly, and appears as a light-coloured narrow space for a 

 short distance along the median line. It then divides to form the two 

 frontal sutures {frs.}, which extend obliquely forward and outward to become 

 obsolete a short distance from the margin of the frons at the insertion of the 

 antennae. 'I'hese sutures also appear as clear lines in the chitinous capsule, 

 and together form a well-defined V, enclosing the portion of the head known 

 as the frons. The frons (fr.) is divided into two by the dai-k brown or black 



