HISTERID.E 225 



Group Americanus. 



In this group, composed principally of fungivorous species, there 

 are at least two very sharply marked divisions, one having five 

 entire elytral striae, besides the sutural, and the other with only three 

 or four entire striae. The species are all rather small, pollutus 

 being the largest, with a maximum length of about 5 mm. Sede- 

 cimstriatus is remarkable in the very coarse deep and crenate elytral 

 striae and punctate elytral apices; it is moderately abundant from 

 Rhode Island at least as far west as Indiana. Perplexus has finer 

 striae, and the entire surface is feebly punctulate. Americanus is 

 very abundant, it has the surface smooth and the striae moderate, 

 the fifth arching at base to meet the sutural as in perplexus and 

 sedecimstriatus. The following is allied to americanus in these 

 respects, but differs very much in the nature of the fifth stria and in 

 the sculpture of the pygidia: 



Hister diffractus n. sp. Very evenly oval, convex, moderately stout, 

 shining, black throughout, the scattered punctulation extremely fine but 

 traceable on the head and pronotum; head with even surface, the stria 

 coarse, entire, rectilinearly transverse in a long line on the front; mandib- 

 ular carinse very feeble; prothorax strongly trapezoidal, with but feebly 

 arcuate sides, more rounded apically, much less than twice as wide as the 

 median length; basal margin finely punctulate; surface even, the outer 

 lateral stria not extending quite to the middle, closely approaching the 

 outer edge, the inner straight, not quite entire; elytra moderately trans- 

 verse, with strongly rounding sides continuous with those of the prothorax, 

 the striae smooth, rather deeply incised, the fifth entire but comminuted, 

 being formed by a succession of punctures and short strise, the sutural 

 incised and with small, widely separated punctures along its bottom; 

 humeral stria represented by a series of fine and very faint punctures 

 medially only, the subhumeral obsolete; inflexed sides nearly flat, tri- 

 striate; propygidium with very widely scattered small punctures, still 

 smaller medially; pygidium convex, smooth, becoming minutely and 

 remotely punctulate basally; mesosternum evenly truncate; anterior 

 tibiae coarsely and sharply tridentate. Length 4.0 mm.; width 3.2 mm. 

 Kansas. 



Differs from americanus in the disintegrated fifth stria and punc- 

 tate sutural, also in the finer and sparser pygidial sculpture. 



Hister biabbreviatus n. sp. More narrowly oblong-oval, more elongate 

 than in americanus, the type piceo-rufous above and beneath, the legs and 

 abdomen clearer rufous; surfaces highly polished, the minute punctulation 

 evident on the head and pronotum, the ambient stria of the former fine 

 but deep, broadly transverse on the front; mandibular carinae fine; pro- 



T. L. Casey, Mem. Col. VII, Nov. 1916. 



