MURIDAI—ARVICOLIN A—ARVICOLA RIPARIUS. 169 
exactly one and three-fifths inches ; and a foot of 0.78, or nearly four-fifths of 
an inch. The majority of the specimens run from 4.25 to 4.50 in length; a 
large proportion run between 4.00 and 5.00. Only eight specimens (about 7 
per cent. of the whole) exceed 5.00, and only twelve (about 10 per cent.) of 
the adult ones fall below 4.00. The proportionally longest tail is as 0.41 to 
1.00, or a trifle over two-fifths of the trunk; the shortest tail is as 0.27 to 1.00, 
or alittle over one-fourth of the trunk; the average tail is to the average trunk 
as 0.37 to 1.00, or about three-eighths. Only a single foot of the 114 exceeds 
0.90, and only three touch this figure; not one falls below 0.70. 
The limits of what may be called normal individual variability are easily 
set from the foregoing figures, and the bounds of possible variation as readily 
perceived for both absolute size and relative proportion of parts. It must 
be observed that we have not yet presumed to inquire whether more than 
one species be represented in the series; but what we claim to have shown 
is that no more than one species can be predicated upon these specimens 
from size and relative proportion of parts, since the absolute dimensions grade 
imperceptibly between the extremes, and the relative measurements are 
inextricably interlaced. 
As a supplement to the foregoing, we subjoin another table of more 
detailed measurements of numerous a/coholic specimens, all from the Eastern 
United States. This table extends and checks the above results to the last 
details of structure, and requires no further comment. 
TabLe XLIIL.—Measurements of forty-five (and list of many other) alcoholic specimens of A. RIPARIUS from 
the Eastern United States. 
| | | i ] 
o From tip of nose} Tail to | Length 
3 to— eud of—| of— 7 
Fl —— : 
A Locality. Collector. ‘ SS aes ae Nature of specimen. 
a) E e|=|S la 
E ; 4 —loa/e)/s)o|/3 | =& 
& 4 2 B o | Fa eee I Ales 
= i 0) eta ey PES TOD (io pe 
o we AIR /O;H | F || e|a) A 
— = ——— | _— eee 
7442 |....| Halifax, Nova Scotia..| J. B. Gilpin. ..... 19. 45) 1. 10/1. 20/4. 20 1. 60} 1. 90/0. 45/0. 840. 50) Alcoholic. 
BP ed lf es bee CO) BARS s bee sae wee e=aececae ns Bao Boos Reod Peed Bete bo ocd ec == do: 
94380 alec ote GW) Sss-Sspnedosse 10) Gonccosedats Jeze-[oee-de aad ba Bara Berd beer) Basel 
4897 od | Meadville, Pa.... ....| J. F. Thickston . --|0. 47/1. 02 1. 30/4. 50/1. 80/2. 00,0, 44/0. 90.0. 45) .. do. | 
2531 4).--.] Labrador ...-...-...- J. Wyman ....... wei[oees|oee [eee ]eee | oe [eee [eeeseee Alcoholic ; young. | 
4967 |....| Lake Superior .....-- George Barnston Blom ase eee eso pe ---|---.|---.!....| Alcoholic, 
9479 =i) coscncecases: Bilereelee cecfeee [one [eee [oeeefeee -.-do. 
9923 Sido cc eee Bal ae base eee |e eee |e: 
OST | eee BdOR 2202-2220 55) |\ seed fcieel pod faceel) 8 [lace |foacy bcd bbetile: 
10574 ?|..-. fee OO Peaseacance Srlkised bso|oced| bes siietd| saps |ocee[Seor|onseOO. 
Tel B. F. Odell .....-- Br Peed Heer sere aes bee-| oe Bead Booed pace le 
| 7597 R. Kennicott -...-- we-[ones|eee w-|ene-[o-- J--- [----]----]e-- do. 
| 7580 mend Ote echo Allies lecealbs |---| == ]0-43}0. 80) -..|..-. do. 
| 
