"Breadth of rostrum above premolars" is easily duplicated in _Lepus_ but in _Sylvilagus_ the control points are difficult to find. Two other persons and I obtained three different measurements, all different from Nelson's measurements, and we thought that Nelson would have obtained different measurements by measuring the same specimen of _Sylvilagus_ at different times. "Depth of rostrum in front of premolars" seems to have been taken perpendicular to the inferior longitudinal line of the rostrum, approximately one-half millimeter anterior to the alveolus of the anteriormost cheek tooth. "Interorbital breadth" was taken across the supraorbital processes, at the narrowest place, but _not_ from the notches medial to the antorbital projections of the supraorbital processes. "Parietal breadth" is the breadth, across the braincase, taken approximately half way between the squamosal root of the zygoma and the external auditory meatus, where there is a lateral bulge in the squamosal bone. On each side of the skull, the calipers rest on the squamosal bone, not on the parietal bone. "Diameter of bullae" excludes the paroccipital process and was taken from the anteriormost part of a tympanic bulla, posterolaterally to the part of that same bulla, that is exposed at the lateral side of the base of the paroccipital process. _Specimens examined._--Total, four, all from Tamaulipas, Mexico, as follows: 88 mi. S and 10 mi. W Matamoros, 3; 90 mi. S and 10 mi. W Matamoros, 1. _Transmitted February 20, 1951._ 23-7414