OF WASHINGTON, VOLUME XVII, 1915 181 



when the hold of the mandibles and legs is released and the 

 body contracted they prevent the segment slipping forward. 

 On a hard surface the caudal lobe of the ninth abdominal seg- 

 ment also assists in backward motion. In this case it is brnt 

 downward and acts as a hook shaped anchor. 



The following technical description will more fully describe 

 the details of these structures and also serve as a means of deter- 

 mining these larvae: 



Horistonotus uhlerii Horn. 



Larva, (pi. 21, fig. a). Elongate, slender and membranous, twenty- 

 seven times as long as wide; color cream white, head ferruginous yellow, 

 pro thorax yellow, mandibles brownish yellow to almost black, spines on 

 legs brownish yellow. 



Head (pi. 20, figs, a, b) elongate cylindrical, length exclusive of mandi- 

 bles, twice diameter, sides subparallel, very highly polished. Front very 

 narrow, sides almost parallel, diameter at middle about one-sixth diameter 

 of head, extending to basal sixth of head, anteriorly dilated to attach- 

 ment of clypeus; bears a pair of fine hairs near pointwhere it is constricted. 

 Clypeus quadrate, a little longer than broad, anterior angles membranous, 

 anterior margin densely fringed with brush of fine hairs, emarginate and 

 armed at middle with a highly chitinized bidentate prong; the dorsuni 

 bears four pair of short erect hairs. Antenna? slightly received in fossa 

 on dorsal surface of mandibles, very large, almost one-third length of head 

 exclusive of mandibles; first joint clavate and but little longer than broad : 

 second joint depressed, cylindrical, wider at distal extremity which is 

 obliquely truncate, truncate surface bearing on inner part the very slen- 

 der and rather short third joint and the accessory appendage, which hit lei- 

 is white and conical; the third joint is about as long as the first joint, cyl- 

 indrical and three times as long as broad, it is slightly curved and directed 

 at right angles to the long axis of the second joint. Mandibles (pi. 20, 

 figs, d, e,f, g) are two-thirds the length of the head, biramous, and multi- 

 dentate; the outer surface (pi. 20, fig. e) is s ightly concave and each ra- 

 mus bears two longitudinal earinse; the inner surface (pi. 20, fig./) of tin- 

 dorsal ramus bears three stout acute teeth and two smaller teeth, tin- 

 latter situated on each side of the lowest tooth; the ventral ramus is un- 

 armed, at the base of the mandible on the inner surface is a broad oval 

 molar area and a row of bristles continue the armature of the upper ramus. 

 The siiliinentiim (pi. 20, figs, a, c) is almost obliterated, by the highly 

 developed maxillary stipes, it is broadened at the anterior half but almost 

 cut off from the mentum by the maxillary stipes which suddenly converge 

 anteriorly, the submentum bears four hairs on its anterior part and a sin- 

 gle pair at its posterior extremity: the mentum is elongate and clavate, 

 and is adorned with a pair of median hairs near its distal end: the labial 

 palpi are about half as long as the mentum, the first joint is twice as long 

 as broad, the second is conical and one-third as long as broad: the maxil- 



