A REVISION OF NORTH AMERICAN CHRYSOBOTHRINI 19 



useless in separating allied species. In the descriptions the base is 

 mentioned as being emarginate, but it is really transversely truncate 

 and simply depressed on the upper surface, where it is covered by the 

 base of the elytra, and when seen from above seems to be emarginate. 

 When the length is being compared with the width, the measurement 

 of the length is taken at the middle and that of the width at the widest 

 part. 



Scutellum. — The scutellum in the North American species is usually 

 very small and triangular, but in a few it is long and strongly 

 acuminate toward the apex. 



Elytra. — The lateral margins are usually coarsely serrate posteriorly, 

 but in a few species they are not or are only vaguely serrate near the 

 apices. The humeral angles are broadly rounded in all the North 

 American species. In a number of western species the surface is 

 clothed with short hairs, which may become inconspicuous, especially 

 on the basal regions, and in poorly preserved specimens there may be 

 some difficulty in seeing these hairs. In some species there are a few 

 hairs on the lateral edge of the elytron, but these species are not con- 

 sidered as having pubescent elytra. The surface is either with or with- 

 out discal f oveae and longitudinal costae ; frequently only the first costa 

 on each elytron is distinct, the other costae being more or less inter- 

 rupted and joined to one another by irregular, transverse, smooth 

 spaces, and in many western species, which live on conifers, the sculp- 

 ture is of little value in separating species. The first costa, as cited in 

 this paper, is the one next to the sutural margin. 



Prostemum. — The surface is usually densely punctured and pubes- 

 cent in the males, and more coarsely punctured and sparsely pubes- 

 cent in the females, but sometimes the surface is similar in both sexes, 

 and may be nearly smooth, especially on the median part. The an- 

 terior margin may be truncate, arcuately rounded, or with a more or 

 less distinct median lobe. This character has been misused by some 

 writers and has caused much confusion in identifying species. In 

 this paper the prosternum is considered as being lobed when there is 

 a lobe in front of the thickened anterior margin, and not when the 

 anterior margin is arcuately rounded. This lobe varies greatly in 

 form and size, sometimes being distinct and abruptly developed, and 

 in other species it is very narrow and inconspicuous. 



Abdomen. — The last visible sternite has the lateral margins either 

 distinctly serrate or crenulate, or entire, but in libonoti and costifrons 

 they are interrupted near the middle. Sometimes the sternite is 

 longitudinally concave or longitudinally carinate at the middle, and 

 frequently there is a dentate, elevated, submarginal ridge on each 

 side. In all our species the apex of the last visible sternite in the 

 male is emarginate, but varying in extent among the species, from a 

 deep quadrangular notch to a shallow, arcuate emargination. In 

 the female the emargination is usually smaller, sometimes truncate or 

 sinuate, and rarely tridentate, and some care must be exercised in 

 using this character in the females, as it seems to be variable in some 

 species. 



The eighth tergite (frequently called the pygidium) is different in 

 the two sexes. Usually the surface is more deeply and coarsely 

 punctured in the female than in the male, and in some species it is 

 longitudinally carinate in the female. 



