When skulls of females are compared, each of the differences mentioned above is found to apply, except that the degree of difference is in some parts greater, for example, in the tympanic bullae. In _primulina_, the bulla is in general like that of the male _noveboracensis_, whereas in the female _noveboracensis_ it is less inflated, especially anteromedially, shorter, relatively narrower, and in ventral view projects little or none below the squamosal floor of the braincase. The breadth of the bulla averages 51 per cent of its length in _primulina_ but only 47 per cent in _noveboracensis_. The bullae project below the basioccipital on the average, for a distance of 2.9 millimeters in female _primulina_ and only 2.3 millimeters in female _noveboracensis_. In _primulina_ the temporal ridges are well developed and fuse to form a low sagittal crest, but in _noveboracensis_ the ridges are absent. Also, in _primulina_ the mastoid processes project farther laterally beyond the braincase. The skull of female _noveboracensis_ is much lighter than that of _primulina_. Average weights of the two are 1.7 and 2.2 grams. The skulls of females of _primulina_ and _noveboracensis_ differ more than do the skulls of males. Compared with the skull of _spadix_, that of the male, and the female, of _primulina_ averages smaller in every part measured. Expressed in percentages of the basilar length, the two depth measurements of the skulls are not significantly different, but, excluding the measurements of the bullae and teeth, the other cranial measurements are less. The main difference in relative proportions is in the tympanic bullae which average only a half millimeter shorter in males of _primulina_ and one and one-tenth millimeters shorter in females. The bullae are, therefore, relative to the basilar length, longer in _primulina_. The skull of _primulina_, then, differs from that of _spadix_ mainly in smaller size and relatively longer tympanic bullae, especially in males. Compared with the skull of _M. f. longicauda_, that of both sexes of _primulina_ averages smaller in every part measured, except in males where the length of the tympanic bulla, and breadth and length of M1 are the same or slightly larger in _primulina_. Relative to the basilar length, the length of the tympanic bullae, and in females only, the depth measurements are greater in _primulina_ but all the others, in both sexes, are less. These ratios reflect the relative narrowness of the skull of _primulina_. Upon direct comparison the narrowness is especially noticeable in the interorbital region, mastoid region, tympanic bullae, and across the zygomata.