112 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
ing, however, those of S¢gmodon, though falling short of those of Hesperomys 
proper. Exceeding in size any other known North American species of Hes- 
peromys, and with the general appearance of Sigmodon or even Mus. 
Further details of this interesting section, the most conspicuous among 
North American Hesperomys, and almost worthy of generic rank, will be found 
under the head of its typical and only known species, the common ‘ Rice-field 
Mouse” of the Southern States. While it does not require for its identifica- 
tion any comparison with its allies, we may here note the position it holds 
among them, after a description of the skull. 
Skull (Nos. 7303, 710, from South Carolina).—The size of the skull 
alone distinguishes it from that of any other North American Hesperomys, 
except, perhaps, H. cal/fornicus, measuring nearly an inch and a quarter in 
length by nearly two-thirds of an inch in zygomatic breadth. It has, how- 
ever, other interesting peculiarities. Prominent among them is the sharp ridge 
or bead into which the superior edge of the orbit is produced. However 
sharp the border of the orbit may be in the smaller Hesperomys, it does not 
form this bead, which seems to characterize chiefly larger forms, as we find it 
in Mus decumanus, Sigmodon hispidus, &c. The anteorbital foramen tends 
to assume a rather unusual shape for a Sigmodont, being subcircular above, 
and running into a narrow slit below; the feature, however, is not very strongly 
marked, and may vary, moreover, with different individuals. We have seen 
skulls of AZus decumanus in much the same condition. As in Mus, Sigmodon, 
and Hesperomys proper, the incisive palatine foramina are long, reaching to or 
even beyond a point opposite the anterior molars; the opposite is shown in 
Neotoma, where the foramina fall far short of the molar series. The great 
backward production of the bony palate that Oryzomys shows does not occur 
in any other North American Hesperomys (where the posterior edge of the pal- 
ate is about opposite the last molar), and perhaps represents one extreme in 
this respect, of which Meotoma, where the palate is scooped out to opposite 
the middle molar, may be the other extreme. The little deep pit, or fossa, on 
either side of the palate opposite the last molar, is as in Sigmodon; but in the 
latter these pits are separated by a median lengthwise process, which is not 
the case in Oryzomys, where the hind border of the bony palate is almost 
perfectly straight crosswise. This backward extension of the palate in Ory- 
zomys is almost exactly the same as in Mus (decumanus); and, altogether, the 
cranial characters, saving the Sigmodont dentition, are certainly the nearest to 
those of typical Mus of any Hesperomys of North America, if indeed they 
