A. W. Rymer Roberts 207 



On the ventral surface of the head, bounded on either side by the 

 epicranial plates, the oval hypostome is found (Text-fig. 1). It projects 

 forward much beyond the opening of the mouth and is composed of the 

 sclerites of the first and second maxillae. Around its margin, forming 

 the boundary of the maxillary stipites, there is a rim of stouter chitin, 

 corresponding to a similar but even stouter rim at the margin of the 

 epicranial plates. The latter originates close to the point of articulation 

 of the maxillary cardo with the tentorium and reaches almost to the 

 base of the mandibles on either side, gradually becoming more slender 

 as it extends forwards. 



Between the two rims of thickened chitin there is a considerable flap 

 of membrane which is ordinarily tucked in between them. At the base 

 of the hypostome, posterior to the submentum and maxillary stipites, 

 there is a considerable field which, save for the two pairs of small sclerites 

 which constitute the cardines, is also membranous. The hypostome is 

 thus capable of considerable extension either in the dorsi-ventral plane 

 or simply forwards, the membranous margin causing it to function as a 

 kind of pouch. 



On either side of the hypostome, within the margins of the epicranial 

 plates, there is a long oblique suture of a brownish colour, extending 

 backwards from the base of the mandibles. 



The two pairs of small sclerites mentioned above are situated near 

 the base of the maxillary stipites. Each one of the outer pair, which is 

 nearly apposed to the stipes, is of an irregular elongate form with its 

 apex pointing obliquely backwards. Posteriorly it is attached to the 

 tentorium at the second branch of the latter. The innermost pair of 

 sclerites, each of which is nearly circular, is situated near the median 

 line and sometimes overlaps the outer pair, the latter being somewhat 

 beneath the general surface of the cuticle. Henriksen (p. 280) considers 

 these smaU sclerites to have no importance and says that the outer one 

 is not attached to the tentorium. As I have found it to be so attached, 

 it must be considered to represent the maxillary cardo, as Ford has 

 described it. No attempt can be made here to homologise the round 

 sclerite. The outer margin of the stipes is rounded, the inner (bordering 

 on the submentum) straight. It is yellow in colour, strongly chitinised 

 and bears at its exterior angle, near the base of the palpiger, two longer 

 and two shorter setae (Fig. 2 c). 



The maxillary palps are composed of four segments, which gradually 

 contract in width from the basal to the apical segment. They are brownish- 

 yellow in colour and are borne on a whitish palpiger which generally 



