124 DAVENPORT ACADEMY OF NATURAL SCIENCES. 



A REVIEW OF THE NORTH AMERICAN SPE- 

 CIES OF IDIOCERUS. 



BY HERBERT OSBORN AND EF.MER D. BALL. 



The members of this genus are easily recognized by their large size, 

 broad, short heads, the eyes exceeding the pronotum in width, which 

 in turn exceed that of the narrow apices of the folded elytra, giving 

 the insects a wedge-shaped appearance. 



The vertex is short and parallel-margined, rounding in front to the 

 face, ocelli on the face between the eyes, just above the origin of the 

 frontal sutures The male antennae usually bear a disc-like swelling 

 near the tip; this is wanting, however, in a few of the European and 

 a number of tiie .American species. The elytra are usually longer 

 than the abdomen and rather narrowly folded behind. There is but 

 one transverse nervure between the sectors and that is often wanting 

 in cratiCi^i, four apical and three anteai)ical cells being the typical 

 number. The elytra alwa\s possess a distinct appendix and the super- 

 numerary cell is present in the wings. 



Specific characters are found in the size and ijosition of the spots on 

 the vertex when present, in the size and shaj^e of the outer anteapical 

 cell, the shape of the facial pieces, the shape of the antennal discs of 

 the male and the general size and color. The genitalia are of less 

 classificatory value in this group than in most of the ByihoscopidcB, 

 the male organs |)resenting few variations that are available for use, 

 their place being somewhat supplied, however, by the antennal discs. 



In the female the shape of the last ventral segment and the length 

 of the ovipositor are important characters in some cases. 



The genus is widely and generally distributed throughout the North 

 Temperate Zone. Europe has over thirty recognized species, and it 

 is probable that that number will be reached in America when the 

 fauna is better known. 



The species of which the life histories are known are all exclusively 

 tree-inhabiting forms in both larval and adult stages and are very lim- 

 ited in their range of trees, being confined to the different species of 



