82 EXTINCT. AND VANISHING MAMMALS 



show an indentation in the outer margin posteriorly, due to the 

 premaxillary bone; the interorbital constriction is less than in 

 subauratus, while the temporal ridges tend to unite to form a 

 distinct sagittal crest posteriorly and show a "higher degree of 

 approximation anteriorly." The interparietal also is somewhat 

 broader. 



The type locality "is situated on Hat Creek, a tributary of 

 the Pit River, which is in turn a tributary of the Sacramento 

 River." Thus, although living in the same hydrographic basin 

 as the form subauratus, its range on the eastern side of the 

 Sierra Nevada is probably bounded by the Pit River Narrows, 

 "a barrier not regularly crossed by beavers." It is possible, 

 according to Benson, that the beavers of the Great Basin may 

 be identical with this form, but the eastern range is not defi- 

 nitely worked out. Grinnell (1933) gives its area of distribu- 

 tion as the Pit River basin in the northeastern corner of 

 California and adds that it is recorded from "Pit River, above 

 Narrows, north to Willow Creek and Steele Meadow, near 

 Clear Lake, and east to Lassen Creek, east of Goose Lake, and 

 to North Fork of Pit River above Alturas these localities 

 being in Modoc County." Its present status is not altogether 

 clear, but Grinnell, Dixon, and Linsdale (1937) have sum- 

 marized all the information they could obtain as to the status 

 of this beaver in northeastern California and the adjacent 

 region up to late 1931, as follows: In September of that year 

 three colonies were known on Fletcher Creek, one consisting of 

 6 animals at Willow Creek Ranch, another of 10 or 12 indi- 

 viduals somewhat farther up Fletcher Creek, and the third 

 and largest in the entire section comprising between 20 and 25 

 beavers near the "Mulkey place." Another colony, consisting 

 of about 15 beavers, lived on South Willow Creek, but a colony 

 formerly living on the North Fork of Willow Creek had ap- 

 parently been destroyed by trapping. About 8 miles north of 

 Canby lived a colony of half a dozen beavers. The largest 

 colony in the county was on Lassen Creek and comprised about 

 50 animals. It extended from a point about 2 miles above 

 where the creek enters Goose Lake for a distance of 2J/2 miles. 

 Four or five individuals lived on Davis Creek where it runs 

 into Goose Lake, and another group of the same size was 

 known on the north fork of the Pit River 16 miles north of 

 Alturas. They formerly (1898) occurred in the Shasta River 



