NO. 7 MUSCULATURE OF COLEOPTERA DORSEY 29 



XXII. LYMEXYLOIDEA 



Hylecoetus luguhris Say, Lymexylidae, adults and larvae were 

 selected for study in this super family. 



The muscles of the labrum in the adult (figs. 129, 130) are repre- 

 sented only by the ventral muscle of the labrum, j. The pharyngeal 

 muscles, p and 11 (figs. 129, 130), occur in paired groups. The 

 muscle of hypopharyngeal bar Y, 10 (fig. 129), lies between the two 

 branches of pharyngeal muscle, p. A small, longitudinal band of 

 muscles, /j (figs. 129, 130), is present; it possibly is homologous with 

 the compressor muscles of the anterior region of the cibarium, /j 

 (fig. 2), of the general plan. They arise medially, adjacent to the 

 anterior margin of compressor muscle group of the cibarium, 12 

 (figs. 129, 130), and are inserted medially and dorsally on the 

 cibarium a short distance anterior to the point of origin. Hypopharyn- 

 geal bar Y (fig. 130) is rather large and furnishes a strong support 

 to the sides of the mouth and to the posterior lateral cibarial region. 

 The lateral dilator muscle of the pharynx, J7 (fig. 130), is long and 

 powerful. The muscle of the prementum, 22 (figs. 130, 131), is the 

 only muscle present in the labium. 



In the larvae of Hylecoetus (figs. 132, 133, 134) the labral muscles 

 are absent; the muscle of hypopharyngeal bar Y, 10, and its branch 

 loA (figs. 132, 133), are especially massive; the cibarial and pharyn- 

 geal muscles are comparatively long and slender. Muscle 10 (fig. 

 133) arises by means of a tendon in the posterior region of the frons. 

 The posterior lateral labial region is furnished with a heavily sclero- 

 tized intralabial brace, IR (fig. 132), the ends of which terminate in 

 the integumental wall. Externally there is a heavily sclerotized U- 

 shaped area present that extends over the dorsal surface of the pos- 

 terior labial region and is continuous laterally with the ends of the 

 intralabial brace, IR (fig. 132). The labial muscles present an unusual 

 plan of arrangement. The prementum is elongate and possesses a 

 small median sclerite in the anterior region (fig. 134). The muscle 

 of the prementum, 22 (figs. 132, 134), which is short and very 

 broad, arises medially along the posterior margin of the tentorial 

 bridge; it is inserted along the base of the prementum. The ven- 

 tral muscle of the labium, 21 (figs. 132, 134), originates medially 

 on the posterior margin of the tentorial bridge and it is inserted rather 

 medially on the posterior edge of the median premental sclerite. 

 The dorsal muscle of the labium, 20 (figs. 132, 134), arises laterally 

 on the inner surface of the posterior end of the anterior tentorial 

 arm ; it is inserted laterally in the anterior region of the median 

 sclerite of the prementum. 



