that although I haven't been able to get back down to Tucson much in recent years I have managed one weekend each summer for the last three years. On each trip I found what was without a doubt an atrox/scute hybrid. Two in the Santa Cruz Valley and one a litte further up the western slope of the Ritas. To me that would at least say they are actually common in some places. Perhaps it was just chance, but I don't think so. I think many others have found them also but did not realize what they were seeing and were in a hurry to get on down the road to find important stuff like tigris and triaspis.