[Rowland Shelley]

That's correct. Those two species occur along the Pacific Coast up to the southernmost islands in the Alaskan Panhandle. The most easily recognized difference between them is the presence of complete paramedian sulci (shallow grooves on both sides of the midline) on most of the tergites (dorsal plates) in gracilis, whereas spinicaudus lacks complete sulci throughout and has only small, incomplete paramedian sulci on the anterior and caudal tergal margins. Looking at these photos, it's hard to tell, but I don't see evidence of complete paramedian sulci, so I think this is spinicaudus. I see marginal sulci (grooves near the margins of the tergites) but not paramedian ones. There isn't much difference between spinicaudus and sexspinosus, but there is a little and it's consistent through the ranges, so the Pacific Coastal species is different from sexspinosus in the Eastern US, and spinicaudus is the oldest available name for it. Because they are very similar, the Pacific species was improperly called sexspinosus for many decades, and it also occurs in Japan. A Japanese myriapodologist, Keizaburo Shinohara, in 1981 was the first to recognize that the Japanese and Pacific Coastal North American species differs from sexspinosus, and he named it Scolopocryptops nipponicus, but I synonymized this name under spinicaudus Wood, 1861, in my 2002 monograph, which is a much older name for the species. I'm sure Shinohara wasn't aware of Wood's work when he proposed S. nipponicus. Rowland Shelley, North Carolina State Museum of Natural Sciences.