_Smilisca sila_ is intermediate between the two species-groups described. The skull is broad; the lateral margins are gently curved, and have a pronounced angularity just anterior to the palatines which results in a broad, truncate snout. The nasals are moderate in size; because of the anterior angularity of the lateral margins, the long axes of the nasals lie parallel to the maxillary. The nasals are only slightly pointed anteriorly, and posteriorly they bear short, blunt palatine processes and medial processes in contact with the lateral corners of the ethmoid. The ethmoid is fully ossified, but does not extend anteriorly between the nasals. The squamosals are moderate in size and extend one-fourth the distance from the dorsal end of the quadrate to the maxillary. The tegmen tympani are relatively large, but proportionately short. The cranial characters utilized in the analysis of species groups (general shape, nature of the nasals, ethmoid, squamosals, and tegmen tympani), together with other characters, such as the relative height and shape of the prenasal processes, the extent of the internasal septum, and the nature of the vomers, frontoparietals, maxillaries and pterygoids are useful in distinguishing the various species (Table 4, Fig. 8), as well as in establishing relationships within the species-groups. Within the _sordida_ group, _S. sordida_ and _S. puma_ can be distinguished by the following characters: The bony part of the ethmoid terminates posterior to the anterior edge of the orbit and is thus widely separated from the nasals by cartilage in _S. puma_. In _S. sordida_ the bony part of the ethmoid always terminates at a level equal to, or slightly in front of the anterior edge of the orbit; therefore, less cartilage exists between the ethmoid and nasals in _S. sordida_ than in _S. puma_. The width of the premaxillary comprises about 30 per cent of the width of the skull in _S. sordida_ and 20 per cent in _S. puma_. The proportion of the length of the skull anterior to the bony part of the ethmoid in _S. sordida_ is approximately 21 per cent, as compared with about 29 per cent in _S. puma_. The prenasal processes are convex in _S. sordida_ and straight in _S. puma_.