In a new study of squamate relationships, Pyron et al. (2013) found Chironius to be polyphyletic, with C, carinatus and C. quadricarinatus forming a clade and with nine other species that were included in the study, forming a second clade. The second clade contains C. septentrionalis and C. scurrulus.
Chironius carinatus is the type species of the genus, thus it and quadricarinatus (and whatever other species not included in the study are related to it) will retain the name Chironius. The second, however, will need a new name, and the oldest name available for the clade will likely be Macrops (= large eyes), a genus established by Wagler in 1830 for Linnaeus' species Coluber saturnius, which is now known as Chironius fuscus.
This result demonstrates how little we actually know about the Neotropical Herpetofauna, the prevalence of species that look similar but are genetically distinct, and the problems caused by the polytypic species concept. Sorting out the details of this promises to be challenging because several of the currently recognized species of Chironius have subspecies, including C. carinatus.
Pyron, RA, Burbrink FT, Wiens JJ. 2013. A phylogeny and revised classification of Squamata, including 4161 species of lizards and snakes. BMC Evolutionary Biology 13:93 doi:10.1186/1471-2148-13-93