SACCOMYID2—DIPODOMYINZ—DIPODOMYS. 521 
Perognathus by the structure of the ear. The present species may be called 
O. longimembris, as the length of the hind limbs and tail is its specific char- 
acter in comparison with O. flava. 
SuBFAMILY DIPODOMYIN Al. 
= Dipodomys (genus), of AUTHORS. 
= Dipodomyina, Couns, Proc. Phila. Acad. 1875, 277. 
= Macrocolini, Branvt, Beit. Kennt. Siug. Russl., vierte Abh., Fortsch. Grupp. Nager, 1855, p. 231 and 
p. 311. 
The characters upon which this group is based having been given on a 
preceding page (p. 494), we may at once proceed to consider the single 
genus by which it is represented. 
Grenus DIPODOMYS, Gray. 
= Dipodomys, t Gray, Ann. Mag. Nat. Hist. vii, 1841, 521. (Type D. phillipii.) 
= Macrocolus, * WAGNER, Archiv fiir Naturg. 1846, Bd.i, 172. (Type WM. halticus.) 
Cnars.—(a. Cranial.) —Skull light, thin, papery, depressed, broad behind 
with swollen curves, tapering in front; rostrum acuminate, produced beyond 
‘incisors; no interorbital constriction; palate plane; occipital surface deeply 
emarginate. Zygomata straight, thread-like, depressed to palatal plane; abut- 
ting against tympanics. Anteorbital foramina represented by a circular per- 
foration of the front of the maxillaries. Large excavated lachrymals. Parietals 
triangular; an elongate interparietal embraced between forks of occipital. 
Squamosals reduced to small plates bounding the orbits posteriorly ; other 
elements of the temporal bone extraordinarily developed, thin, and bladdery, 
their sinuses of nearly as great capacity as the cerebral cavity ; the mastoids 
especially enormous, constituting nearly all the occipital and the greater part 
of the superior (behind the parietals) surfaces of the skull; the tympanics 
proportionally inflated, with large non-tubular orifice of meatus; the petrosals 
bullous, their apices in contact across the median line below the basisphenoid. 
Tympanics, mastoids, and parietals entering orbits. Occipital singularly 
reduced and narrowed, bent into three planes at right angles; supra-occipital 
bifurcate to inclose an interparietal; paroccipitals narrow, flange-like ;_basi- 
* Three special papers, substantially the same, differing in some particulars, viz.:— 
‘On a new Genus of Mexican Glirine Mammalia.” < Ann. Mag. N. H. vii, 1841, pp. 521, 522. (The 
original notice; genus named on p. 521; species D. phillipii, same page.) 
‘On a New Glirine Animal from Mexico.” < Rep. Brit. Assoc. Ady. Sci. for 1841, 1842, Trans. of the Sec- 
tions, p. 70. (Same orthography of name.) 
“On anew Glirine Animal from Mexico.” < Amer. Journ. Sci. and Arts, xlii, 1842, pp. 334, 335. (Editorial 
reproduction of the last; name D. phillipsii on p. 335.) 
| Special paper :— 
“Macrocolus, eine neue Nagergattung aus der Familie der Springer.” < Arch. fiir Naturg., zwolfter 
Jahrg. Bd. i, 1846, pp. 172-178. (Species M. halticus named, p. 176.) 
