Puebla: Atencingo, KU 39626. Skull In studying the osteology of the genus _Conophis_, I have examined two complete skeletons (one _C. vittatus_ and one _C. lineatus_); two additional skulls of _C. vittatus_ and _C. lineatus_; and 24 sets of dentigerous bones, representing all of the species. Terminology of the skeletal elements is that of Duellman (1958), Parker (1878), Radovanovic (1937) and Szunyoghy (1932). The drawing of the right side of the skull of a specimen of _Tomodon lineatus_ that appears in Jan and Sordelli (1881:liv. 50, pl. 2, fig. 34) is of little value due to its small size and lack of detail. The skull of _Conophis_ is typical of a relatively unspecialized colubrid snake. Skulls of _Conophis lineatus concolor_ and _C. vittatus_ closely resemble each other. The following description is based primarily on the skull of _C. lineatus concolor_ (UMMZ S-778). The elements are discussed in the following order: nasal region, cranium and associated elements, maxillo-palatal-pterygoid arch, mandible, dentition, and vertebrae. [Illustration: FIG. 6. The skull, lacking dentigerous bones, of _Conophis lineatus concolor_ (UMMZ S-788) showing (A) dorsal, (B) lateral, and (C) ventral views. × 3.] _Nasal region._--The premaxillary is relatively heavy and has a concavity posteroventrally. The lateral processes slope downward, but remain fairly thick, and do not project far laterally. This shape (fig. 6) tends to strengthen the nasal region; this anterior strengthening may be a reflection of the fossorial habits of these snakes. There are no posterior processes of the premaxillary; thus the line of fusion with the nasals and septo-maxillaries is broad. The nasal plate is more than twice as long as wide. The nasals are relatively flat above, although each curves slightly downward medially and fuses into the medial nasal septum; laterally each nasal is narrower and deflected downward, forming a small dorsal shield over the nasal cavity. The septo-maxillaries are closely associated with the vomers and form the cavity in which the organ of Jacobson is situated. The broad medial part of the septo-maxillary forms the roof and anterior border of the cavity, whereas the anterior part of the vomer contains the main part of the capsule and forms the posterior and most of the lateral borders of the cavity. The vomer has a thin anterior ridge that gradually disappears before it reaches the border of the premaxillary. The vomer is approximately U-shaped, when viewed from below. It has no posterior process and does not articulate with the parasphenoid; there is a sizeable gap between the two bones. The septo-maxillary has a lateral process that terminally is directed slightly anteriorly.