MURIDAS—SIGMODONTES—SIGMODON. 3: 
whereas they do not appear to afford grounds for any such subordination. 
Thus, Onychomys seems to us fully as different from Hlesperomys proper as 
Sigmodon is; and we should judge the same to be the case with such forms 
as Abrothrix and Oxymicterus. But as we are not now undertaking a critical 
revision of the whole sigmodont tribe, we prefer to accept the groups as we 
find them, provided they are established with any considerable show of reason, 
rather than present decided innovations; and for the present, in order to 
bring out the groups in the strongest relief, we accord generic rank to some 
that probably we should reduce to subgenera upon final survey of the whole. 
The principal diagnostic points of the skull of Sigmodon are those men- 
tioned in a preceding paragraph. The shortness of the skull, in comparison 
with the great width, resulting from the widely divergent zygomata; the short, 
swollen, rostral portion; the arched frontal profile; the curious little pointed 
process of the lamellar plate of the maxillary that bounds the foramen 
(wanting in other groups we have examined—even in Oryzomys) ; the posi- 
tion and peculiar sculpture of the palatal shelf; the small bulle ossez; the 
bead on the orbital edges,—all are strong characters, in peculiar combination. 
We might easily describe several additional, more minute features, but this 
seems unnecessary. The following table shows the size, proportions, and 
variations of the skull of the single species of the genus we have examined. 
TasLE VI.—Measurements of fourteen skulls of species of SIGMODON. 
n 
te lies Se || 
Locality. 2 3 a 2 2 2 2 z Remarks. 
3 P| et aC ge ah RS ES Rl 
= cy o Ss = Ea) eB 3° 3 BR Ke) 
A y | N 4 =| | vay pa) iS} J] A 
4763 | Georgia..-.....--.-.-... 1.37 | 0.52 | 0.80 0.20 | 0.55 0.26 | 0.75 | 0.93 | 0.37 | 0.26 | hispidus ; adult. 
CO) eeottl) Seem oaebosebeccbed 1,27 | 0.59 | 0.73 | 0.18 0.48 | 0.22 | 0.66 | 0.83 | 0.32 | 0,22 hispidus ; adult. 
167 5H uw doe eas Seeks 1.40 | 0.54 | 0.82 | 0.21 | 0.55 | 0.25 |...... 0.95 | 0.38 | 0.25 | hispidus ; adult. 
3 Pit) er Ee Bee 1.20 | 0.52 |.----- | 0.20 | 0.45 | 0.24 | 0.70 | 0.80 | 0.30 | 0.95 | hispidus ; adult. 
2022 | South Carolina Heel S525] |AAeces| sere ce) |S |S te ae 0.72 | 0.92 | 0.34 | 0.23 | hispidus ; adult. 
GES |) Tay sccucecssesacse =" |(Sreone ieeees| jones 0.20 | 0.42 0.17 | 0.67 | 0.76 | 0.24 | 0.20 | hispidus ; adult. 
12147 | Mohave Valley, Cal.....} 1.30 | 0.53 | 0.75 | 0.20 | 0.52 A app-b es | 0.73 | 0.90 | 0.34 | 0.25 | hispidus ; adult. 
Tey PT ee ate cece cosacotesses| Pacaee beeoes 0.77 | 0.20 | 0.50 | 0.24 }...--. [pea 0.29 | hispidus ; adult. 
1667 | Coahuwa, Mexico ..-.-..|..---. saat 0.78 | 0.19 | 0.50 | 0.26 | 0.70 | 0. | 0.25 | * berlandieri.” 
12151 | Matamoras, Mexico.... | 1.15 ...... \Psssae 0.19 | 0.44 | 0.15 | 0.62 lo | 0.23 | “ berlandieri.” 
9671 | Tehuantepec, Mexico .. | 1.40 | 0.54 | 0.75 | 0.20 | 0.57 | 0.24 | 0.72 0.90 | 0.33 | 0.25 | * berlandieri. ” 
O65 Nes dots 3 Se eek 1.27 | 0.49 | 0.80 | 0.20 | 0.50 | 0.23} 0.69 | 0.84 | 0.32 | 0.24 | ‘ berlandieri.” 
Sites | Hi) tase Soemescecsa 1.20 | 0.48 | 6.70 | 0.19 | 0.45 | 0.19 | 0.60 | 0.77 | 0.29 | 0.20 | “ berlandieri”; youngish. 
7210 | Orizaba, Mexico .-..... 1.15 | saacte 0.70 | 0.18 | 0.42 | 0.19 | 0.60 | 0.77 | 0.29 | 0.20 | “tolteeus”; youngish. 
Dentition Selecting an average adult example, as No. 4763, in which 
the teeth are full-grown, yet not so worn as to deface the pattern, we find as 
3M 
