Six skulls of _meridionalis_ were matched with six skulls of _chiapensis_ having approximately the same amount of wear on the teeth, and the series were compared, pair by pair, in various cranial characters. In five of the six pairs _meridionalis_ had a less inflated braincase, and smaller postpalatal foramina, and in each of the six pairs _meridionalis_ had a greater depression in the frontonasal region and posteriorly more acute incisive foramina. Four external measurements and nine cranial measurements were compared using the series of _meridionalis_, the series of _chiapensis_ from Guatemala, and Hooper's (1952:213) measurements of seven _chiapensis_ from central Chiapas. The lesser average and maximum total length of skull in _meridionalis_ than in either series of _chiapensis_ suggests that _meridionalis_ has a smaller skull. Externally, the lesser total length of _meridionalis_ is largely owing to its shorter tail; there is little difference in length of head and body between _meridionalis_ and _chiapensis_. The longest tail among our _meridionalis_ is shorter than the shortest tail among the _chiapensis_ (disregarding two Guatemalan specimens of _chiapensis_ that probably had injured tails). The interorbital breadth of _meridionalis_ is on the average greater and the depth of cranium is less than in _chiapensis_. There is some overlap in the range of each of these two cranial measurements, but in all _meridionalis_ the interorbital breadth exceeds 42 per cent of the depth of cranium, and in all _chiapensis_ is less than 42 per cent. The length of the incisive foramina in _meridionalis_, expressed as a percentage of the total length of the skull, is usually greater than in _chiapensis_. One of our specimens (KU 71389) contained four embryos that measured 5 mm. in crown-rump length. _Measurements._--Selected measurements of the holotype, followed by the average and extreme measurements of six specimens of _meridionalis_ (including the holotype) from the vicinity of the type locality are: total length, 154, 152.0 (148-154); length of tail, 82, 82.0 (81-83); length of hind foot, 17, 18.0 (17-19); length of ear from notch, 13, 13.3 (12-14); total length of skull, 21.4, 21.13 (20.3-21.7); zygomatic breadth, 10.0, 10.38 (10.0-10.6); breadth of braincase, 10.1, 10.17 (9.9-10.4); depth of skull, 8.2, 8.00 (7.8-8.3); interorbital constriction, 3.7, 3.53 (3.4-3.7); breadth of rostrum, 3.8, 3.75 (3.6-3.9); length of rostrum, 7.4, 7.33 (7.1-7.7); length of incisive foramen, 4.6, 4.47 (4.2-4.6); length of upper molar tooth-row, 3.2, 3.32 (3.2-3.5). Corresponding measurements of a specimen from 11 mi. SE Darío are: 153, 82, 18, 13, 20.7, 10.3, 10.1, 7.8, 3.4, 3.6, 7.2, 4.3, and 3.2.