NO. 10 MORPHOLOGY OF GNATHOTRICHUS SCHEDL 49 



Tarsus. — The tarsus (fig. 26, Tar) is composed of five joints or seg- 

 ments. They are not articulated by hinges with each other but they 

 are movable by means of inflected connecting membranes. The first 

 three segments (k, 1, m) are subequal in length and shape. The basal 

 segment or basitarsus does not show any special armations such as 

 occur in other genera. The fourth segment (n), the smallest of the 

 tarsus, resembles somewhat in shape the trochantin. This segment 

 which is often highly modified in the Scolytidac, is short and knob- 

 like in GnafJwtrichiis. The apical segment (o) is longer than seg- 

 ments one to three, more slender and slightly curved. Except the 

 fourth, all tarsal segments bear at least a few hairs scattered over the 

 entire length. The third segment also bears a plushlike arrangement 

 of hairs apically. 



Prefarsus: the terminal segment. — The terminal foot structure (fig. 

 26, Ptar), which has been called praetarsus, Krallenglied, unguis, 

 ungula and pretarsus by different authors, bears two simple claws (p) . 

 The areolium (q) is membranous and heartshaped. 



THE WINGS 



As in all the Scolytidae, Gnathotrichus Eichh. has well developed 

 elytra or mesothoracic wings and hind or metathoracic wings. The 

 development of the metathoracic wings would indicate, as has been 

 found to be the case, that the species of this genus are good fliers. No 

 attempt will be made in what follows to speculate on the functions 

 of the different sclerites of the articulation of the wings since the 

 author has had no opportunity to make observations on them. Merely 

 a description-of the different parts will be given which it is hoped may 

 be of value for future taxonomic and physiological studies. 



MESOTHORACIC WINGS OR ELYTRA 



The mesothoracic wings consist as usual of two layers of integu- 

 ment, both of which are chitinized, the outer layer however being 

 much thicker than the inner layer. The space between these two 

 layers contains the tracheal and circulatory systems. The punctures 

 which mark these wings externally indicate, according to Hopkins, 

 the points of union between the two layers. The form and general 

 structure are shown in figures i, 3, 16 and 27. The elytra when closed 

 and viewed from above are as wide as or slightly narrower than the 

 pronotum, with the sides subparallel, slightly tapering toward the apex 

 and broadly rounded behind, the extreme external margin subacute. 



