Figure 2. Early derivatives of the large-scaled Sceloporus. Lettering style follows Fig. 1. Phylogenetic interpretations follow Hall (1973): The undescribed orcutti group species and S. licki, both included as a subspecies under orcutti by Smith (1939), are closely similar to nelsoni and pyrocephalus, placed by Smith (1939) in the small-scaled radiation. Larsen and Tanner (1974, 1975) also place these two species close to the small-scaled species groups scalaris, siniferus and variabilis, as I have defined them (Fig. 1). S. orcutti proper is the only other large-scaled species to retain the primitive 2n=34 sceloporine karyotype. Three major sequences of chromosomal derivation trace their ancestry from a hypothetical 2n=32 ancestor, derived by centric fusion (probably involving the sex chromosomes) from a 2n=34 species which must have been morphologically similar to the present orcutti proper. The three sequences are: C. the clarki sequence, involving the fixation of 4 macrochromosomal centric fissions; D. the very recent sequence within the morphological species, Sceloporus grammicus, maximally involving the fixation of 5 macrochromosomal and 1 microchromosomal centric fissions and a polymorphism for a 6th macrochromosomal fission; and E. the sequence leading to the 2n=22 Sceloporus, which maximally involves fixation of 5 microchromosomal fusions (tracing from the 2n=32 karyotype) and microchromosomal pericentric inversions (unless some of the fusions were tandem instead of centric).