PROC. ENT. SOC. WASH., VOL. 24, NO. 6, JUNE, 1922 157 



INSECTS 



Protocephalon. 



Antennal segment. 

 Intercalary segment. 



Mandibular segment, with 

 paragnaths. 



First maxillary segment. 



Second maxillary or labial 

 segment. 

 (Last segment of head.) 



First thoracic segment. 



a Antennafers. 

 af Antefrons. 

 an Antennules. 

 cl Clypeus. 

 e -Eyes. 

 g Genae. 

 / Labruin. 



CHILOPODS 



Acron. 

 Preantennal segment. 



Antennal segment. 

 Intercalary segment. 

 Mandibular segment. 



First maxillary segment. 



Second maxillary seg- 

 ment. 

 (Last segment of head.) 



"Poison claw" segment. 

 (Loosely associated with 

 the head.) 



HIGHER CRUSTACEA 



Protocephalon. 



Antennular segment. 

 Antennal segment. 



Mandibular segment, 

 with paragnaths. 



First maxillary segment . 



Second maxillary seg- 

 ment. 



First maxilliped seg- 

 ment. (Last segment 

 of head.) 



ABBREVIATIONS. 



//> Labial palpi. 

 md Mandibles, 

 mdp Mandibular palpi. 

 mp Maxillary palpi. 

 mx Maxillae. 



Ocelli. 



Parietals. 



Postfrons. 



oc 



pa 

 Pf 



EXPLANATION OF PLATE 15. 



Fig. 1. Frontal view of head of isopod crustacean Lygida exotica. 

 Fig. 2 Same of isopod crustacean Gnathia maxillaris (male). 

 Fig. 3 Same of pterygotan insect (psocid) Thyrsophorus speciosus. 

 Fig. 4 Same of amphipod crustacean Talorchestia lonncornis. 

 Fig. 5 Same of apterygotan insect Machilis sp. (M. polypoda?). 

 Fig. 6 Same of apterygotan insect Nicoletia texana (?). 

 Fig. 7 Same of apterygotan insect Lepisma sp. 

 Fig. 8 Same of isopod crustacean Asellus communis. 



