Intergradation was noted in still other cranial details. In the heavy, relatively straight zygomatic arches, a majority of the skulls resemble those of planirostris, although some show the elongated zygomatic processes of the squamosals that are characteristic of virgineus. Some skulls show a tendency toward birdseyei in the widely spreading posterior regions of the zygomatic arches. The nasals for the most part are as in planirostris. Intergradation between all three subspecies is shown in the extension of the premaxillae posterior to the nasals. Some skulls show the lateral concavity of the jugals which is characteristic of virgineus. The tympanic bullae are variable but on the average are intermediate between those of planirostris and birdseyei, but more as in the latter. The size of the pterygoid hamulae is like that of planirostris, but the shape of the interpterygoid space is more like that of birdseyei. The size of the molariform teeth is as in birdseyei. The incisors are intermediate between those of planirostris and birdseyei, but more like those of birdseyei.
Eighteen specimens from St. George and its environs, on the north side of the Virgin River, agree with the twenty-six specimens just described, except that they show more evidence of intergradation with birdseyei in slightly darker color, length of hind foot, length of nasals and alveolar length of the upper molar series.
One specimen from three miles south, two from two miles southwest, another from four miles southeast of St. George, and four immature animals from Short Creek Road south of the town of Virgin, all on the south side of the Virgin River, are darker than topotypes of planirostris and show intergradation with trumbullensis to the south. In size they are likewise closer to the latter race. They intergrade with trumbullensis in the size and shape of the zygomatic arches and tympanic bullae. In the majority of cranial details, however, they are like planirostris to which they are here referred.
One specimen, a skin only, from Danish Ranch, 5 miles northwest of Leeds, north of the Virgin River is an intergrade in size and color between birdseyei and planirostris, but referable to the latter.
Three specimens from the East Entrance, and three from near the east entrance to Zion National Park are much darker than topotypes of planirostris. All of these animals are in worn pelage, thus allowing a great amount of the black underfur to show, which gives a markedly darker color. The unworn hair is only slightly darker than that of the topotypes. The cranial details prove these animals to be intergrades between planirostris and trumbullensis. They resemble trumbullensis in size of tympanic bullae, extension of the premaxillae posterior to the nasals and shape of the nasals. The majority of the cranial details are as in planirostris to which they are here referred.
When Goldman (1938:337) named Thomomys bottae nicholi from northern Arizona he referred twelve specimens from St. George, Washington County, Utah, to his newly named race. He noted that the animals from this region intergrade with planirostris. I have had occasion to study one-fourth of the material available to Goldman for his original description of nicholi. For his specimens listed as from St. George, the exact locality of capture, which is so essential in this distributional study, was not given. All of the specimens that I have seen from the Biological Surveys Collection are from the south side of the Virgin River, while St. George itself is on the north side. As noted earlier in this account there are differences between the gophers from the two sides of the Virgin River in this area. Those from the north side are intergrades between birdseyei, planirostris and virgineus, while those from the south side are intergrades between planirostris and trumbullensis.
Goldman (loc. cit.) mentioned several times that the skulls of nicholi were nearly indistinguishable from, or closely resembled those of, trumbullensis. Color was the only truly diagnostic character mentioned by Goldman. My study reveals the same differences and likenesses found by Goldman, but I consider color alone insufficient basis in this instance for establishing a new subspecies, and regard Thomomys bottae nicholi as a synonym of the earlier proposed name, Thomomys bottae trumbullensis.
The animals from the south side of the Virgin River, labelled as from St. George, Washington County, heretofore referred by Goldman to nicholi, are intergrades between trumbullensis and planirostris and along with other specimens from the same place are referable to the latter race.
Specimens examined.—Total, 68, distributed as follows: Washington County: Danish Ranch, 5 mi. NW Leeds, 1; Zion National Park, 2 (M. V. Z.); Grotto Camp, Zion National Park, 4,300 ft., 6 (N. H. M. S. D.); Springdale, 3,400 ft., 4 (K. U.); near Short Creek Road, S town of Virgin, 4 (R. H.); St. George, N Virgin River, 2,950 ft., 21 (4, M. V. Z.; 8, R. H.; 9, N. H. M. S. D.); Santa Clara Creek, 3 mi. SW St. George, 2,800 ft., 26; St. George, S Virgin River, 5 (2, M. V. Z.; 3, U. S. N. M.); 2 mi. SE St. George, 2,950 ft., 2 (N. H. M. S. D.); 3 mi. S St. George, 1 (C. M.); 4 mi. SE St. George, S Virgin River, 1 (R. H.); 6 mi. S St. George, 2,700 ft., 6 (K. U.). Kane County: East Entrance Zion National Park, 5,725 ft., 3 (N. H. M. S. D.); near East Entrance Zion National Park, 5,500 ft., 3 (N. H. M. S. D.).