PHALACRID^E 55 



specimens of vittatus from Dakota, taken at the same time and un- 

 questionably of one species, I find both these forms of the curve, the 

 width of the metasternal process and development of the mesoster- 

 num at its sides varying greatly. Generally the deflexed tip of the 

 prosternal process is simple, but in one of these same specimens the 

 extreme deflexed apical margin is reflexed to form a narrow shelf, 

 very obvious when viewed vertically. 



Some species, now widely separated in the above table, should 

 properly be grouped together in an arrangement based more upon 

 physiological affinities, such as fallaciosus, irregularis and rufipes, 

 which, because of the peculiar elytral sculpture of minute longitudi- 

 nal scratches, should be placed in the same group as pruddeni, 

 wickhami, calamis and cessus, notwithstanding the fact that the 

 last four species have but a single true discal stria on each elytron. 

 These seven species would be distinguished as a section from all 

 other American forms of Olibnis, by having the punctures of the 

 two lateral series of the elytra slightly dilated and lunate as a rule, 

 being a departure from the general rule in the genus, that all the 

 serial punctures are minute and simple or subelongated points, and 

 a reversion toward the usual type of punctures seen in other genera 

 of the family. But even here fallaciosus forms an exception, as the 

 punctures of the lateral striae are in that species minute simple 

 points like the more dorsal punctures that is, so far as observed in 

 several examples. 



The mandibles in this genus are arcuate, acute on the outer edge 

 and hollowed or flattened throughout beneath, the upper surface 

 flattened or feebly impressed and with a few coarse punctures on 

 the external slope. The apex is tridentate, the middle tooth acute 

 and projecting much further than the others, which are small. 



Stilbus Seid. 



In North America this genus is fully as developed as Olibrus, 

 perhaps more so, and the species are rather more numerous in the 

 southern parts than elsewhere, while Olibrus and Phalacrus are more 

 evenly distributed in latitude and relatively not so abundant in 

 the warmer regions. The essential characters of the genus are the 

 rather short hind tarsi, with only very moderately elongate second 

 joint, great development of the mesosternum before the metasternal 



