DIAPERINI NORTH OF MEXICO — TRIPLEHORN 423 



closely approximates P. nigratum, with which it shares the characters 

 of the conspicuously punctured pronotum and elytral intervals. 

 The essential difference between the two lies in the distance separating 

 the eyes, which seems constant in the two forms. In P. nigratum, 

 this distance is always subequal to 1.7 times the longer axis of one eje, 

 while in the other form, it is at least 3 times the eye length. The 

 lateral punctures of the basal three abdominal sternites are ex- 

 tremely coarse and widely separated in the new form. I have seen 

 only three specimens, all from Mexico. 



All of the above three taxa look very much alike superficially, 

 especially since they all have the identical system of antennal colora- 

 tion. In addition, they are inseparable on the basis of the male 

 genitalia. It is possible that they are all variations of the same 

 species, but since they are readily distinguishable, they may be re- 

 garded as distinct until additional contrary information is available. 



The system of antennal coloration mentioned above is by no means 

 restricted to members of this P. nigratum complex. It has been a 

 source of confusion which persists even into the present paper. There 

 are a number of South and Central American forms which also ex- 

 hibit the character, but all of these studied to date were found to be 

 distinguished from one another, or at least broken down into work- 

 able units, by the structure of the male genitalia. 



The principle variations exhibited by P. nigratum are the relative 

 convexity of the prosternum, which is subject to a rather wide degree 

 of variation and should not be relied upon as a taxonomically useful 

 character, and the relative degree of punctation of the elytral intervals. 

 Many specimens appear to be covered by a fine velvety pile, rendering 

 it difficult or impossible to distinguish punctures; there is also a 

 decided tendency for grease to clog the punctures, with the same 

 effect. In instances of doubt, it is best to clean specimens thoroughly 

 with ether and a small brush. 



Types. — Platydcma javus Horn (not Fabricius, 1801). This name 

 is included in the synonymy since it is the first reference in the liter- 

 ature to the present species. Horn (1870) referred specimens of 

 this species to P. janus (Fabricius), described from Peru. Since no 

 specimens of P. nigratum have been seen south of Nicaragua, it seems 

 best to assume, as suggested by Champion (1886), that P. janus 

 represents another species. The Fabrician types were not seen, but 

 the material upon which Horn's revision is based (ANSP) is typical 

 of P. nigratum as defined above. Neomida nigrata Motschoulsky. 

 Type in UMMZ. Two Texas specimens sent for comparison cor- 

 responded fully regarding all characters (Kelejnikova, in litt.). In 

 addition, she pointed out that Motschoulsky failed to indicate that 



