Ill 



STRUCTURAL CHARACTERS. 



The structures of the ipid beetles are discussed in this paper only very 

 briefly for the purpose of illustrating the keys for determination. The termin- 

 ology already employed in literature is made use of here so far as possible. 



GENERAL CHARACTERS OF THE BODY. 



The size varies in species of our fauna from 1 mm. in Crypturgus and 

 Pityophthorus to 9 mm. in Dendroctonus. The shape is cylindric, varying from 

 very stout, as in males of Anisandrus, to moderately elongate, Gnathotrichus, 

 or elongate-oval in outline from above, as in Leperisinus. 



The colour is usually dark reddish brown or black when mature; all species 

 are yellowish when first transformed, and turn darker as the integument becomes 

 more strongly chitinized. A few genera, as Leperisinus and Pseudohylesinus, 

 have patches of scales of varying shades of brown and grey. Species of Trypo- 

 dendron have the pronotum and elytra varied in black and shades of yellowish- 

 brown. 



The vestiture varies greatly and presents interesting characters. It varies 

 from long slender hairs to very minute, fine, almost invisible pubescence, to 

 very short bristles or to scale-like hairs, and finally to stout, flattened, plain or 

 ribbed scales. The hairs may be simple or show many plumose and palmate or 

 tuffed variations. Very stout spatulate setse as well as spines are developed 

 on the tibise. In the ambrosia beetles of all genera, including Platypus, very 

 long, slender sense-hairs are developed in patches on the labial palps. These 

 hairs are evidently related to the habit of fungus-feeding and present an 

 interesting case of convergence. Varying frontal or declivital pubescence may 

 be of secondary sexual significance. 



The armature consists chiefly of stout setae and spines on the tibise; lunar 

 rugosities or asperities on the front of the pronotum, more or less strongly devel- 

 oped; lunar rugosities about the base of the elytra, sometimes accompanied by 

 an elevated elytral base; and teeth or spines on the interspaces of the declivity. 

 The declivital spines are particularly important in the classification of such 

 genera as Pityogenes, Ips, and Xyleborus. An epistomal carina or process, and 

 frontal tubercles, are developed in some species. The integument is nearly 

 always strongly chitinized, except in such degenerate forms as the males of 

 Anisandrus. 



The Sculpture. The surface of the body is pitted with setose punctures of 

 varied structure; the longer setse or hairs of the elytra are almost invariably 

 borne by the interstrial punctures, and the minute pubescence from the strial 

 punctures. The margin of the punctures is variably elevated into granules, 

 rugosities or spines. The lunar rugosities of the pronotum and the declivital 

 serrations are enormously developed marginal granules ; they seem always con- 

 nected with a setose puncture of which they are the greatly elevated front 

 margin. The elytra are variably striate with the interspaces often convex, or 

 carinate behind, and variably rugose. In addition to bearing punctures, granules 

 and setse, the head is frequently very finely aciculate, and any part of the integu- 

 ment may be finely reticulate. 



THE HEAD. 



The head is somewhat quadrate and prominent, visible from above in the 

 Hylesininoe and Eccoptogasterince, subglobular and more deeply embedded in 



