238 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



is a small triangular piece in Idiocerus as well as in Pyrilla. The 

 clypeus is divided into a small anteclypeus and a highly developed 

 postclypeal region in both insects. On the sides of the clypeus in case 

 of Idiocerus, there is a maxillary plate which is divided by a longi- 

 tudinal suture into two parts. The maxillary plate of Pyrilla is not 

 divided by a longitudinal suture. Between the maxillary plates and 

 the clypeus there is a plate which has been termed the mandibular 

 plate by Weber and earlier workers and the lorum by Snodgrass and 

 Butt. The nature of this plate is in dispute and according to some 

 workers it is a part of the head capsule, having been demarcated from 

 the clypeus. Snodgrass, however, regards it as belonging to the hypo- 

 pharynx. According to the present writer, the loral plates are not 

 identical in all the Homoptera. In Idiocerus they appear to be de- 

 marcated from the head capsule, and are external, while in Pyrilla 

 they are derived from the hypopharynx and are internal. 



Tentorium (fig. i). — The tentorium of Homoptera has been de- 

 scribed by Snodgrass, Muir, Myer, Weber, and Davidson. The 

 present studies show that in Idiocerus the tentorium consists of a 

 pair of 3-armed bars, and the central body of the tentorium is absent. 

 In Pyrilla the tentorium is complete and consists of the central body 

 lying closely approximated with the transverse maxillary bar and has 

 three pairs of usual arms, dorsal, anterior, and posterior. 



Mouth parts. — The hypopharynx of Hemiptera is a highly com- 

 plex and well-developed structure. Its study has come into the lime- 

 light recently through the works of Weber and Snodgrass. It consists 

 of a lobelike body lying below the clypeus. Basally it is continued into 

 a pair of wings which are on their sides basally coalesced with the 

 tentorium. Dorsally, at the junction of the anteclypeus, the hypo- 

 pharynx is produced into a troughlike structure known as the 

 sitophore, which forms the floor of the food canal. In Pyrilla (fig. 2) 

 at its junction with the epipharynx the hypopharynx forms a pair of 

 lateral plates, fused with the anteclypeus. Since the protractor mus- 

 cles of the mandibular stylets arise from this plate, the author regards 

 them as lora. On the ventral aspect of the hypopharynx there is the 

 salivary syringe, which has an elaborate propelling arrangement con- 

 sisting of a piston worked by muscles. The cavity of the syringe, 

 as shown by Weber in Pentatoma and Palonema and as observed by 

 the author in Pyrilla, is provided with a valve inhibiting the reverse 

 flow of the saliva. 



Epipharynx. — The epipharynx of Homoptera has been much neg- 

 lected. Adequate attention to this structure has recently been given 



