NO, 7 MUSCULATURE OF COLEOPTERA — DORSEY 1 3 



//. The labium is a good example of the prementum with two divi- 

 sions I and 2 (fig. 33). The muscle of the hypopharynx, ip (figs. 33, 

 34), the dorsal and ventral muscles of the labium, 20 and 21 (figs. 

 33> 34) > and the muscle of the prementum, 22 (fig. 34), are all present, 

 well developed, and take their origin on the tentorial structure. In 

 the specimen of Staphylinae the muscle of the prementum, 22, is in- 

 serted on the prementum at the base in the same plane as the dorsal 

 and ventral muscles of the labium, 20 and 21. The prementum is not 

 divided into two parts as in Silpha. The cibarial, pharyngeal, and 

 hypopharyngeal muscles are much the same as those in Silpha, with 

 a few variations. The labral muscles are absent ; a tendon arises on 

 the anterior tentorial arm, dorsal region, and extends anteriorly to 

 be inserted basally and laterally on the nasale in a manner very simi- 

 lar to the insertion of the ventral muscle of the labrum, 3, in the adult 

 Creophilus villosus Grav. 



VI. HYDROPHILOIDEA 



Sphaeridium scaraboides Linn., Hydrophilidae (figs. 35, 36, 37), 

 is the adult form studied. The muscles, though well developed, are 

 reduced in number. Muscle / (fig. 35) possibly corresponds with 

 the compressor muscle of the labium, i, in Periplaneta; the insertion 

 has become changed from the ventral wall of the labrum to a sclero- 

 tized mesal extension of the torma which is continuous with the dor- 

 sal wall of the anterior region of the cibarium. The ventral muscle 

 of the labrum, j (figs. 35, 37), arises on the distal end of the dorsal 

 branch of the anterior tentorial arm and is inserted in the usual way. 

 The dorsal dilator muscles of the cibarium, 5, 6, and y, are absent. 

 The anterior tentorial arms are joined by a sclerotized suboesophageal 

 brace, SB (fig. 37) ; a lateral dilator muscle of the pharynx arises 

 on this brace. The dorsal and ventral muscles of the labium, 20 and 

 21 (figs. 36, 37), both take their origin in the anterior area of the 

 postmental region. 



Sphaeridium bipustulatum Fabr. (figs. 38, 39, 40) and Hydrous 

 triangularis (Say) are the larvae studied in the family Hydrophilidae. 

 In Sphaeridium the labral muscles are absent. The dorsal dilator 

 muscles of the cibarium, 6 and 7 (figs. 38, 39), are present; muscle 6 

 is long, 7 compact and linear. The dorsal dilator muscles, p and 11 

 (fig. 39), are well developed as is also the muscle of hypopharyngeal 

 bar Y, 10 (fig, 39). Bar Y is continuous with the sclerotized sub- 

 pharyngeal area. The three muscles 36, 57, and 38 (fig. 39) are 

 probably maxillary muscles. Muscle jd arises laterally from the pos- 

 terior region of this sclerotized subpharyngeal area and J7 and 38 



