302 AMERICAN PACHYBRACHYS (cOLEOPTERa) 



though seemingly trivial, is unusually constant, seldom difficult 

 to interpret, and of great value in the tabulation of the species. 



Eyes. — The eyes vary greatly specificallj^ in size and degree of 

 approximation and are therefore of very great aid in classification. 

 In order to make full use of them, however, it is necessary to 

 express their distance asunder more exactly than by the terms 

 "near" or "remote" as hitherto, and I have for this purpose 

 chosen as a standard of comparison either the length of the basal 

 joint of the antennae, or the vertical width of the upper lobe of 

 the eye. In the greater number of species the eyes in the male 

 are separated by a distance from one to two times the length of 

 the basal antennal joint. If the distance be less than the length 

 of the basal joint the eyes may properly be called near, and if 

 greater than twice the length of this joint they may be called 

 remote; these terms, however, are not much used in the following 

 descriptions. It should be remembered that since the width of 

 the front between the eyes is measured in terms of the length of 

 the basal antennal joint of the insect itself, and since the length 

 of this joint is often somewhat greater in the male than in the 

 female, the results cannot be directly compared. 



Antennae. — These organs are remarkably uniform in structure, 

 and aside from some variation in length and thickness offer very 

 little in the way of specific differences. In the aberrant mic- 

 rops the antennae are sensibly thickened externally, but in all 

 other species they are virtually filiform. The first joint is 

 always stouter, more or less broadly oval; the second somewhat 

 similar in form but much smaller; third more slender and longer 

 than the second, gradually wider apically; the next two or three 

 similar but increasing in length, the outer five or six subequal in 

 length, the tenth usually visibly shorter; the eleventh appendicu- 

 late. In hepaticus and microps these organs are scarcely half 

 as long as the body in the male, while in males of Ivridus, trinota- 

 tus, nuhilus and several others they are nearly or quite as long 

 as the body. In the great majority of species the antennae are 

 about three-fourths the length of the body in the male, the 

 length — with very few exceptions — being somewhat shorter in 

 the female. In the descriptions following, the length in terms of 

 the body is usually given, and frequently the length of the tenth 

 joint in terms of the width, this ratio being a fair index of the 



