The milliped order Siphonophorida in the United States and northern Mexico

New localities are reported to detail the distributions of the order Siphonophorida and the family Siphonophoridae in the southwestern and southcentral United States, and northern Mexico. The northernmost sites are in Los Angeles County, California; Yavapai County, Arizona; and Coryell County, Texas. The Siphonorhinidae is represented by only one genus and species, Illacme plenipes Cook & loomis, known only from northern San Benito County, California, the northernmost ordinal record. Congeneric starus is confirmed for Siphonacme lyttoni Cook & loomis, in Arizona, and S. pseustes (Chamberlin), in Sonora, Mexico; Californizonium Verhoeff is synonymized under Siphonacme Cook & loomis. Diagnostic illustrations are presented for I. plenipes, S. lyttoni and pseustes, and Siphonophora limitare Loomis and texascolens Chamberlin & Mulaik.