602 



THE MONTHLY BULLETIN. 



fine pattern ; the buff tone is deeper below than above ; close inspection shows the 

 hairing of the tail to be concentrically banded, three black bands and four light ones, 

 the outermost black band being broadest, and the outermost light one constituting a 

 peripheral whitish fringe. 



Color variations. — As far as we can see, the two sexes are identical in coloration, 

 save as caused by the greater rate of wear to which the pelage of the female is 

 subject during the season when the young are being reared. Wear progresses in some 

 cases until most of the colored ends of the hairs are gone, and a dingy light brown 

 color is acquired, including also the tail. Molting begins anteriorly and progresses 

 backward. 



The material we have studied seems to show but one decided molt in adults each 

 year, and this takes place during July and August. Young, however, seem to undergo 

 two molts in the first six months of their lives. When one-third grown their pelage 

 is characterized by a fluffy texture and a yellowish tone of color, but the general 

 pattern is closely similar to that of adults ; when nearly full grown the young are 

 smooth-coated and show rather brighter tones of brown and clearer white shoulder 

 patches that even fresh-pelaged adults. 



There are not infrequent special, or "sport" variations, in the Beechey Ground 

 Squirrel, such as albinos, either complete or partial, which have been reported from 

 time to time. We have been told of "black" ground squirrels ; and there is in the 

 Museum of Vertebrate Zoology an adult male, from Stanislaus County, taken by 

 W. C. Jacobsen, January 30, 1918, which is of a curious light pinkish -buff tone of 

 coloration, save for the outermost concentric black band on the tail and for the 

 whitish shoulder patches and a suggestion of dappling on the back. t 



The color description given above was taken from specimens from the vicinity of 

 San Francisco Bay. Specimens from other parts of the general range of the 

 Beechey Ground Squirrel depart from this slightly in different respects. Two speci- 

 mens at hand from Marysville Buttes, Sutter County, are of paler, grayer tone of 

 general color. A series of skins from the western slope of the central Sierra Nevada 

 averages whiter underneath and darker brown on middle of back. Examples from the 

 southern San Joaquin Valley are paler in tone of .coloration and exhibit whiter 

 shoulder patches, thus evidently constituting intergrades towards the Fisher Ground 

 Squirrel. A series from the coast district of southern California, from Santa 

 Barbara to San Diego, shows darker brown back, but whiter under surface of body, 

 and the white shoulder patches are more conspicuously contrasted. Some San 

 Diego County examples in rather worn pelage show a curious reddish tinge on the 

 rump. 



Measurements. 1 — Average and extreme measurements, in millimeters, of twenty 

 full-grown specimens from west-central California are as follows : Ten males : total 

 length, 435 ( 405-475) ; tail vertebrae, 164 (150-175) ; hind foot, 57 (52-60) ; ear 

 from crown, 20.5 (17-24) ; greatest length of skull, 59.1 (56. 9-61.1) ; zygomatic 

 breadth, 36.9 (35.0-39.2) ; interorbital width, 14.1 (13.3-15.0). Ten females: total 

 length, 423 (400-460) ; tail vertebra?, 162 (150-175) ; hind foot, 57 (55-58) ; ear 

 from crown, 18.4 (16-20) ; greatest length of skull, 56.2 ( 53.8-59.5) ; zygomatic 

 breadth, 35.8 ( 34.3-37.6) ; interorbital width, 13.9 (13.0-14.7). 



It will be seen from the above figures that females are decidedly smaller bodied than 

 males though in tail length they are about the same. The skulls of the oldest individ- 

 uals, particularly males, show greatest general size, greatest zygomat ; c breadth (as 



1 The measurements given throughout the present paper have been taken according 

 to the following methods. The external dimensions are those recorded on the label 

 attached to the skin and were taken from the freshly killed animal by the collector 

 in each case. Total length is the distance from the tip of the nose to the tip of the 

 last vertebra of the tail (which is also practically the tip of the tail without the 

 hairs), the body and tail being straightened out but not stretched; tail vertebrae is 

 the length of the tail alone (again without hairs), from a point on upper side at base 

 where tail can be bent at right angles to back, to tip of last vertebra ; hind foot is 

 measured when extended flat at right angles to leg, \ from heel to tip of longest claw ; 

 ear from crown is the distance vertically from top of head at inner base of ear to 

 extreme tip of ear, not including hairs. The cranial measurements were all taken by 

 the senior author, with parallel calipers reading to tenths of millimeters, from 

 cleaned skulls. Greatest length of skull is taken parallel to axis of skull from ante- 

 rior tips of nasals to most posterior point or points on skull (this in some skulls falls 

 on the condyles, in some on the lambdoidal ridge) ; zygomatic width is the greatest 

 width of skull at right angles to axis, from the outer surface of one zygomatic arch 

 to the outer surface of the other ; interorbital width is the least distance between the 

 eye-sockets, but not counting the little notch usually present in ground squirrels on 

 each edge of the interorbital portion of the roof of the skull. 



10 



