DIAPERINI NORTH OF MEXICO — TRIPLEHORN 405 



sternum prominent, convex, horizontal, its apex bluntly rounded, 

 anterior portion (in front of forecoxae) strongly carinate; metaster- 

 num finely and densely punctate, except caudo-lateral portion; ab- 

 domen coarsely and densely punctured, forming longitudinal wrinkles 

 laterally except two apical segments where punctures are fine and 

 sparse, not forming wi'inkles laterally. Male genitalia with ventral 

 portion of lateral lobes continued backward as a single spine in- 

 complete at apex (pi. 4, fig. 28). No apparent external sexual di- 

 morphism. Measurements: length 5.6-7.3 mm.; width 3.1-4.2 mm. 



Remarks. — I encountered in a number of collections occasional 

 individuals and short series of specimens which at first I thought 

 represented extreme variations of P. americanum. Many had been 

 identified by various workers as P. americanum and P. oregonense. 

 When these were segregated, critically examined, and plotted distri- 

 butionally, it became evident that I was dealing with a strikingly 

 different form, which I regard as a distinct species. Its resemblance 

 to both of the above mentioned species cannot be denied; however, 

 it resembles neither of them entirely, being more or less intermediate 

 in regard to several characters. 



It may be distinguished from P. oregonense by its more parallel 

 elytral margins and the relativel}^ complete outermost elytral striae, 

 the more conspicuously punctured elytral intervals, the more shallowly 

 impressed frontal depression, and the somewhat larger average size. 



From P. americanum it may be separated by the trapezoidal pro- 

 notum with its straight or very feebly arcuate, narrowly expanded, 

 and less strongly reflected, lateral margins, which almost always 

 lack even traces of the broad impression on each side behind the 

 middle so characteristic of P. a7nericanum. 



The genitalia suggest a closer affinity with P. americanum than 

 with P. oregonense, but external characters point first toward one and 

 then the other. The head and thorax strikingly resemble those of 

 P. oregonense, while the form and sculpture of the elytra are equally 

 as strongly suggestive of P. americanum. 



The distance separating the eyes ranges from almost t\vice to less 

 than the longer axis of one eye and is unreliable as a taxonomic 

 character. 



The peculiar prolongation of the apical antennal segment men- 

 tioned above is most perplexing. In a series of 105 specimens from 

 Modoc County, Calif., 22 show an extreme awl-shaped segment 

 (pi. 6, fig. 54), 33 show a tendency toward this modification but 

 developed to a lesser degree, 25 show merely a pointed apical segment, 

 while 29 show a rounded type which I consider more or less typical 

 of a member of this genus. 



