A new dune-dwelling lizard of the genus Leiocephalus (Iguania, Leiocephalidae) from the Dominican Republic.

We describe a new species of Leiocephalus from the coastal dunes of Bahía de las Calderas in the southwestern Dominican Republic. In external morphology, Leiocephalus sixtoi sp. nov. is most similar to L. schreibersii and L. inaguae. Leiocephalus sixtoi differs from L. inaguae in having a U-shaped bony parietal table (vs. V-shaped in L. inaguae), 3 or 4 enlarged postcloacal scales in males (vs. 2 in L. inaguae), most scales on snout posterior to internasal scales rugose to keeled scales (vs. smooth in L. inaguae), and a patternless throat in males, spots on the throat in females (vs. throat with dark streaks and bars in males and females of L. inaguae). Leiocephalus sixtoi differs from L. schreibersii in having the scales of the lateral fold only slightly smaller than adjacent scales (vs. scales of lateral fold distinctly smaller than adjacent scales), having prominent caudal crest scales in adult males (vs. caudal crest scales of moderate size, even in very large males in L. schreibersii), a pattern of dark gray bars on a grayish brown background in the region above the lateral body fold (vs. dense turquoise blue mottling with heavy suffusion of red pigment in L. schreibersii), a darker dorsal ground color (vs. paler in L. schreibersii), and a red iris in adult males (vs. pale grayish blue in adult male L. schreibersii). Leiocephalus sixtoi differs further from L. schreibersii in several osteological characters as follows: in L. sixtoi the nasal process of the premaxilla reaches to mid-level of the bony external nares (vs. to level of posterior margin of the bony external nares in L. schreibersii), lacking a constriction at the base of the nasal process of the premaxilla (vs. such a constriction present in L. schreibersii), and having a reduced nasal-prefrontal contact leaving the nasal processes of the frontal bone exposed (vs. nasal and prefrontal bones contact one another, thereby obscuring the nasal processes of the frontal bone in L. schreibersii). We designate SMF 26228, an adult male from Saint Marc, Province Artibonite, Haiti, as the neotype of L. schreibersii.