AMERICAN COLEOPTERA. 101 



I. Elytra widely embracing the abdomen at sides; the ventral surface about 



one-third the width of the elytra, the latter polished and impunc- 

 tate Gibbiini. 



Entirely glabrous above, eyes subfrontal. ventral segments four, hind tro- 

 chanter two-thirds as long as the femur Gilihium. 



Head and thorax densely squamose, eyes lateral, ventrai segments five, 

 hind trochanter scarcely one-third as long as the femur. .Meziuill. 



II. Elytra much less widely embracing the abdomen, the ventral segments nearly 



equal in widtli to the elytra (except Sphsericus), elytra always punc- 

 tate and pubescent Ptinini. 



Elytra confusedly punctate, ventral surface but little more than half as wide 



as the elytra Spliin-icus. 



Elytra punctate-striate, ventral surface nearly equal in width to the elytra. 



Au ten use 9-jointed, size minute Pit hum. 



Antennae 11-jointed. 



Eyes relatively very small, nearly semi-circular, their lower segment 

 with the lenses imperfectly developed and clothed with scales; scu- 

 tellum very small or completely invisible; elytra globose, similar in 

 the sexes; metasternum scarcely as long as the second ventral seg- 

 ment; posterior trochanters reaching the margin of the elytra when 

 directed outward. 

 Prothorax narrowed but not constricted behind. ..TrigonogeniuM. 



Prothorax constricted behind Nipt us. 



Eyes rounded, not squamose inferiorly, scutellum distinct, trochanters 



not reaching the elytral margin. 



Eyes rather small in both sexes; prothorax feebly constricted close to 



the base; elytra similar in the sexes; metasternum subequal in 



length to the second ventral segment; first and second ventral 



sutures nearly obliterated at middle Niptinus. 



Eyes moderately large, often very large in the male; prothorax 

 strongly constricted posteriorly ; elytra parallel or nearly so in the 

 male, oval in the female of the subgenus Ptinus ; metasternum much 

 longer than the second ventral segment in the male ; ventral sutures 

 distinctly impressed Ptinus. 



Gibbiini. 

 The two genera constituting this tribe are at once distinguishable 

 from all others by the greatly contracted ventral surface; the infla- 

 ted polished and impunctate elytra and the densely hairy or scaly 

 under surface and appendages. On account of the very short sterna 

 the legs are placed close together, especially so in Gibbium, in which 

 the acetabula are almost perfectly contiguous from front to back. 

 The reduction of the number of ventral segments in Gibbium 

 appears to result from the coalescence of the first and second. 



TRANS. AM. ENT. SOC. XXXI. MARCH, 1905. 



