ordinary waste-ball method of applying carbon bisulphid is due to the fact that sudden elevation in the course of the burrow, of as much as two feet in some cases, prevents the heavy gas from reaching the animal. This condition was found to occur much more frequently than is generally supposed.
The instances just cited all suggest that the present knowledge of our ground squirrels is far from complete, and they serve to emphasize the above contention that a more thorough knowledge of this subject is essential to securing the most intelligent and efficient methods of control of these our chief rodent pests. It is the purpose of the present paper to supply the information available from all sources in as much detail as it has proven feasible for the authors to secure it at this time. The facts and inferences are given just as they came, irrespective of whether or not they show obvious and immediate economic bearing. They are here available to everyone who is concerned with methods of control.
ACKNOWLEDGMENTS.
The present paper has been prepared at the suggestion of Mr. G. H. Hecke, California State Commissioner of Horticulture, and Mr. W. C. Jacobsen, Superintendent of Rodent Control under this commission. Both these men have rendered many valuable helps during the progress of our work and have co-operated to facilitate its final publication. Their emphasis all along has been upon the need of a summary of the facts relative to rodent natural history at this particular time, when efforts from every direction are being concentrated upon the problem of increased crop production.
Upon the facilities and auspices of the Museum of Vertebrate Zoology of the University of California the writers have been dependent for the opportunity of carrying through their undertaking; and behind this has been the continual financial and moral support of the founder and constant patron of the Museum, Miss Annie M. Alexander. The collections of specimens and the field records contained in this Museum, gathered during the past ten years, have been absolutely indispensable to the present accomplisliment. A total of 1263 study skins of ground squirrels taken within this state have been examined in the course of our work.
In the spring and summer of 1911, two field assistants from the United States Public Health and Marine-Hospital Service were assigned by Dr. Rupert Blue, then Surgeon in Command, San Francisco, to accompany the Museum party working in south-central California, for the purpose of increasing the common knowledge of the distribution and manner of occurrence of the rodents of the region. Acknowledgment is here made for the use of certain facts from the manuscript report of that year's work made to Dr. Blue by the Director of the Museum.
During the past year, Dr. W. C. Billings, Surgeon, in temporary charge, United States Public Health Service, San Francisco, has very greatly aided us in having his field men send us specimens of ground squirrels, both alive and dead, for experimentation and study.
To Professor Harvey M. Hall, of the University of California, we are indebted for identifying numerous seeds obtained from the cheek-pouches of ground squirrels.
Through special provision of the State Commissioner of Horticulture we have been fortunate in being able to have the accompanying five colored plates of ground squirrels drawn by the eminent animal artist, Mr. Louis Agassiz Fuertes. We thank Mr. Fuertes for the special pains he has taken in executing these drawings.
Color terms used in our descriptions are taken from Ridgway's Color Standards and Color Nomenclature (1912).
Information used by us from published sources is credited through the system of author, year and page references to the list of "Literature Cited" which appears at the end of this paper. The authority for important information obtained from field notebooks or from letters is given in parenthesis together with the abbreviation for the word manuscript—"MS."
Joseph Grinnell.
Joseph Dixon.
September 13, 1918.
KEY TO THE GROUND SQUIRRELS OF CALIFORNIA.
1. Size large: body alone more than 9 inches (228 mm.) long; tail more than 6 inches (152 mm.), not counting hairs; ears tall and rather pointed; tail bushy.
2. A blackish brown wedge-shaped patch on middle of back between shoulders Douglas Ground Squirrel (p. 52).
2'. No blackish patch on back.3. Tail longer: without hairs, about 8 inches (203 mm.); no sharply defined triangular whitish patch on each shoulder Rock Squirrel (p. 58).
3'. Tail shorter: without hairs, 7½ inches (190 mm.) or less; a more or less sharply defined triangular whitish patch on each shoulder.4. Size larger: body alone more than 10¾ inches (273 mm.) long; general tone of coloration darker Catalina Island Ground Squirrel (p. 49).
4'. Size smaller: body alone less than 10¾ inches (273 mm.); general tone of coloration lighter.5. Coloration pale in general tone, near light cinnamon-drab; shoulder patches clear silvery white and more extensive Fisher Ground Squirrel (p. 44).
5'. Coloration somewhat darker, near wood brown; shoulder patches duller white and less extensive California Ground Squirrel (p. 9).
1'. Size medium or small: body alone less than 9 inches (228 mm.); tail less than 6 inches (152 mm.), not bushy; ears low and rounded, or else reduced to mere rims.
6. Body with conspicuous lengthwise stripes; coloration varied.7. One white stripe on each side of body; under side of tail conspicuously white; head not more or less yellowish or coppery.8. Smaller: body alone 6 inches (152 mm.) or less; general coloration grayish drab Desert Antelope Ground Squirrel (p. 94).
8'. Larger: body alone 6¼ inches (158 mm.) or more; general coloration light clay color.9. Size slightly greater; tone of color slightly darker, more deeply clay color Nelson Antelope Ground Squirrel (p. 103).
9'. Size slightly less; tone of color slightly paler, more buffy Los Baños Antelope Ground Squirrel (p. 110).
7′. Three stripes on each side of body, one white and two black; head more or less yellowish or coppery.10. Tail longer: without hairs, about 3½ inches (89 mm.).11. Tone of coloration lighter; middle of back more of an ashy brown Inyo Golden-mantled Ground Squirrel (p. 89).
11'. Tone of coloration darker; middle of back more of a cinnamon-brown Sierra Golden-mantled Ground Squirrel (p. 83).
10'. Tail shorter: without hairs, about 3⅛ inches (79 mm.) San Bernardino Golden-mantled Ground Squirrel (p. 92).
6'. Body without any stripes: general coloration nearly or quite uniform.12. Size larger: body alone more than 7 inches (178 mm.).13. Larger: body about 8½ inches (216 mm.); middle of back not bright reddish-brown, but grayish-brown Oregon Ground Squirrel (p. 59).
