294 MEMOIRS ON THE COLEOPTERA 



and hitherto confounded with it. Sobrina is a species distinct from 

 obliqua, as shown not only by type of ornamentation, but by a 

 constant difference in the clypeal horn, which is much smaller, 

 shorter and more triangular in sobrina. There is great varia- 

 bility intraspecifically in the form of this process, but I find there 

 are bounds to this variability in each species; in arizonica, for 

 instance, it is always very conspicuous and longer than wide, but 

 varies only from the parallel and narrower, to the very strongly 

 apically expanded and broadly truncate, form, never becoming 

 small and triangular as it is in sobrina, to which arizonica is other- 

 wise related. 



The coloration of the elytra in the obliqua type is surprisingly 

 constant, but in nitida it is extremely variable, in fact not only in 

 this direction, but in sculpture, pubescence, frequent symmetrical 

 impressions of the pygidium and structure of the anterior tibiae, 

 the large series of nitida in my collection has cost me a dispropor- 

 tionate expenditure of time and patience, with frequent doing and 

 undoing of efforts to guess what nature has really accomplished in 

 the way of evolving species in this group. I finally gave up the 

 problem and left the material in a single piebald series, except the 

 three examples serving as types of the subspecies proposed above, 

 which seemed too exceptional in one or more ways to form part of 

 the series from any rational viewpoint. Those forms called species 

 above, I thoroughly believe to have that status, the only point 

 involving doubt being the mutual relationship of angustula and 

 parvula, and it is not well to be too positive in such a case as this. 

 The punctata section of Pelidnota is almost identical in regard to 

 uncertainties of taxonomic values. 



In looking over the Mexican species, many of which are assigned 

 in error to mutabilis as simple varieties by Mr. Bates, it becomes 

 evident that palliata G. and P., and aurantiaca Bates, are mere 

 varieties of sobrina, which is a distinct species, and that robusta 

 Bates, is a variety of obliqua Burm., another distinct species as 

 indicated above. I thought at first that aurantiaca might be 

 identical with the form described above as arizonica, as its general 

 appearance is strikingly similar, but the description of the clypeal 

 horn as triangular to quadrate shows that it is not the same as 

 arizonica, where the horn is very large, nearly always strongly 



