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.
Compared with the skull of M. f. neomexicana that of both sexes of primulina averages smaller in every part measured. Excepting the measurements of the teeth, most of the other measurements are constantly larger. Relative to the basilar length, the length of tooth-rows and length of tympanic bulla are more, but excepting the depth measurements, the others are less. Still other differences are, in primulina, less well-developed sagittal crest, anterolateral corner of bulla rounded rather than "square," and in males a transversely convex rather than flat interorbital region.
Compared with M. f. frenata and M. f. texensis, the skulls of males of primulina differ in being smaller in every part measured but relative to the basilar length, have longer tooth-rows, a lesser zygomatic breadth and are less constricted interorbitally.
Compared with the skull of M. f. olivacea, those of both sexes of primulina average smaller in every part measured, have shallower (dorsoventrally) tympanic bullae, a lower sagittal crest and slightly weaker postorbital processes on the frontals. Relative to the basilar length, the several cranial measurements are about the same.
Comparison of the skull with that of M. f. arthuri has been made in the account of that subspecies.
Remarks.—The first specimens of this race known to have been preserved in study collections are one in the United States National Museum, taken at Bridge, Carroll County, Missouri, many years ago by J. Burbage, and less than a dozen specimens preserved before 1900 from eastern Kansas in the University of Kansas Museum of Natural History. In 1913 Hartley H. T. Jackson bestowed a name on this animal on the basis of two specimens taken by him in southwestern Missouri. Later, through the efforts of Charles D. Bunker, and his associates at the University of Kansas, nearly 100 specimens were saved from eastern Kansas, principally from Douglas County. In the course of the present study, Lawrence V. Compton obtained a topotype for the California Museum of Vertebrate Zoölogy, and with the assistance of Mr. B. G. Roberts, a good series of specimens from Boone County, Arkansas, was preserved in the same museum. In the early years of the 20th Century, the late B. H. Bailey at Coe College, Iowa, collected specimens from that state. The specimens from these several sources suffice to give a relatively clear idea of the characters of this subspecies.