508 MONOGRAPHS OD NORTH AMERICAN RODENTIA. 
TABLE I.— Measurements of eleven specimens of PEROGNATHUS PENICILLAIUS. 
7 : { 
a 
Bi From tip of nose to— ae io Length of— 3 5 
= sy 
3 Localit 7 i 5 2 = 
ie aay | g S| fe: | Meas 
5} z 3 pallets yas eee z 
rs y| Ss ea) esas oll peed lingers gore pel efehan\l ae iB 
*2676 | San Francisce Mountains, Ariz ..---.-.--- Selim | OEOTO NY oa ERG PRE eft)! te. = 0.49 | 1.00 | 0.30 | Mounted. 
1332 | Colorado River, Cal .-.--..-.---.--..----- =o Peaee YW ence | 3800) P3260" | Fee VOL G0) oa Diy. 
1933) ont souma. Cals. ---) eos. oo Sess (soe || emer -----| 3.65 | 4.15 | 0.40 | 0.95 | 0.30 |...-do. 
1349 |'(Colorado Desert, 'Cal_..--- -----.-=---<.-- a= |10;0)] 0590700 120500) Sets ||P=s= =. [ata= |eenee [enna Alcoholic. 
8910 | Camp Grant, Ariz. ...-. Pee eee ee 2 | 0.60 | 0.95 | 1.10 | 2.90 | 3.50 | 4.00 | 0.35 | 0.85 | 0.30 |....do. 
492'a) Mojave Village, Ariz is do | 0.65 | 1.00 } 1.25} 3.30) -.-. |..-... 0.45 | 1.00 | 0.33 |..--do. 
49240) ...... UO a 3e sae sod sa Seas eee oso- | 2 | @.55 | 0.80-} 1.10 | 3.60 | 3.50 | 4.00 | 0.40 | 0.95 | 0.35 |... do. 
4924e 5 o | 0.55 | 099 | 1.10 | 3 00 | 4.00 | 4.60 | 0.40 | 0.90 | 0.30 |... do. 
4924d & | 0.60 | 0.95 | 1.20 | 2.90 | 4.25 | 4.80 | 0.40 | 0.95 | 0.35 |... do. 
4924e) co | 0.65 | 0.95 | 1.20 | 3.50 | 4.30 | 4.90 | 0.40 | 1.00 | 0.35} .. do. 
49247|...-.. GUE rece noo-Reepostecceans Paccencoces o | 0.60 | 0.90 | 1.20 | 3.60 | 4.49 | 5.00 | 0.40 | 1.00 | 0.35 |... do. 
* Measurements of length and of tail-verteb: 2 from Woodhouse. In its present state, the tail, as well as can be judged, 
is about 4.50 long, exclusive of the terminal pencil, which is half an inch more. The dry measurements are not reliable. 
Taking the last seven’ sets of measurements of the foregoing table (all 
made from sexed specimens in the flesh, and taken by the same person,* so 
that a source of error which lies in different methods of measurement is 
a differ- 
a fair rate of variability for a species. The tail, as usual, varies 
avoided), we observe that the total length varies from 2.90 to 3.60 
ence of 0.70 
more than the body, or, in this instance, about an inch, whether the vertebrae 
alone are considered, or the terminal pencil be taken into account. The 
relatively shortest tail (vertebrae alone) is half an inch longer than the head 
and body, or, with the hairs, an inch longer. The relatively longest tail 
(vertebree alone) is an inch and a quarter longer than the head and body; 
with the hairs, nearly two inches longer. Muck as usual, the rate of relative 
variability is greater than that of absolute difference in dimension. The soles 
vary a tenth of an inch in length, or about 94 per cent. of their average length. 
Other smaller measurements give corresponding results The rates of varia- 
tion which are determined for the present species are doubtless equally appli- 
cable to others of the genus of which I have no alcoholic specimens. 
Upon the supposition that the other allied species described in this paper 
are really distinct from P. penicillatus, this has a remarkably restricted geo- 
graphical distribution. So far as I am aware, there are no specimens extant 
from beyond the limits of the Colorado Valley in that portion of its extent 
*In measuring tails, I take as nearly as possible the true length, by placing one leg of the com- 
passes snugly above the anus. The length to which the tail projects beyond the bedy-hairs, or its osten- 
sible dimension, is considerably less. ; 
