INTRODUCTION 241 



more primitive stage. The last joint, althougli of similar 

 length to the two preceding it, generally presents a much larger 

 sensory surface. The joints forming the club can be spread out 

 or rolled into a sort of ball, with -the leaflets brought close 

 together inside. The leaflets are not thin plates but finger-like 

 jirocesses clothed, except at the base, with hair. 



The upper surface of the head has invariably a ridge at the 

 inner edge of each eye (the supraorbital ridge) and a median 

 elevation, sometimes produced into a shaip horn projecting 

 forwards. From the central elevation usually extend a ridge 

 to right and left (the i)arietal ridge) and a pair of diverging 

 frontal ridges, each ending in a frontal tubercle. The supra- 

 orbital ridges may be united behind the parietal ridge by 

 another (supraoccipital) ridge, and may be continued to the 

 front margin of the heatl or a little beyond it. The processes 

 resulting, although usually symmetrical, are not ahvays so, 

 the left one being sometimes longer than the right, as in 

 Aceraiu.s. This may also be the case with another (umer) 

 jjair of marginal processes, that on the left side being some- 

 times longer than that on the right. 



The eyes are lateral, prominent and fairly large. The organs 

 of tlie mouth are ex])Osed, very well developed and highly 

 chitiixized. The mandibles are large and provided with sharp 

 biting teeth from the tips to the base of the imier surface, 

 a very peculiar feature being a movable tooth, with shaqj 

 transverse edge, attached near the base of each mandible. 

 This appears to be alwaj's separately articulated, except in 

 a few AiJLACOCYCLiN^. The labrum is cliitmous and extruded, 

 forming a large flap lying within the hollow formed by the 

 mandibles. Upon the lower surface of the head the labium is 

 greatlj' develo])ed and assumes a ])eculiar form. Both ligula 

 and mentum are hard and chitinous, and the labial palpi are 

 broad and compact, the 2nd joint much enlarged. The 

 mentum is very broad and flat, and jjroduccd into a wing-like 

 lobe on each side, partly enclosing the ligula and i)a]pi. The 

 maxillae are long and both inner and outer lobes are produced 

 into sharp homy hooks. The maxillary palpi are slender 

 and mobile. 



Key to the Subfamilies of Pass.\lid.e. 



Body cylindrical, front coxae very prominent, 



not distinctly .separated Aulacocyclinie, p. 241. 



Body more depressed, front coxae not very 



jjrominent, distinctly separated Pa.i:'ialina\ p. 24G. 



Subfamily AuLACOCYCLiN.a:. 



Body cylindrical, not flattened, very smooth, with only very 

 scanty and inconspicuous hair. Head symmetrical, the 



B 



