SACCOMYID^— DIPODOMYIN^— DIPOUOMYS. 



521 



Perognathus by the structure of the ear. Tlie present species may be called 

 O. longiinfrnhris, as the length of the hind limbs and tail is its specific char- 

 acter ill comparison with O.JUiva. 



Subfamily D IPODOMYIN^. , 



= Dipodomyi (KcmiH), of AuTitoiiH. 

 = DipodomijiKW, Codes, Proc. Pbila. Acad. 1875, 877. 



=iIacroa)lini, Brandt, Bvit. KcDut. Siiuf;. UubsI., viette Abb., Fortsoh. Qrapp. Nugor, 18&5, p. 831 aud 

 p. 311. 



The characters upon which this group is based having been given on a 

 preceding page (p. 434), we may at once proceed to consider the single 

 genus by which it is represented. 



Genus DIPODOMYS, Gray. 



= I>0M(7omva, tORW, Ann. Mag, Nat Hist. Tii, 1811, 521. (Type D. phitlipii.) '' ' 



= Macrocolui, * Wao.nbii, Archiv fUr Vatnrg. 1846, Jld. i, 172. (Type M. haWcH$.) 



Chars. — (a. Cranial.) — Skull light, thin, papery, depressed, broad behind 

 with swollen curves, tapering in front ; rostrum acuminate, produced beyond 

 i j'oors; no interorbital constriction; palate plane; occipital surface deeply 

 emarginate. Zygomata straight, thread-like, depressed to palatal plane ; abut- 

 ting against tympanies. 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, conf?tituting nearly all the occipital and the greater part 

 of the superior (behind the parietals) surfaces of the skull ; the tympanies 

 proportionally inflated, with large non-tubular orifice of meatus ; the petrosals 

 bullous, their apices in contact across the median line be.ow the basisphenoid. 

 Tympanies, mastoids, and parietals entering orbits. Occipital singularly 

 reduced and narrowed, bent into three planes nt right angles; supra-occipital 

 bifurcate to inclose an interparietal ; paroccipitals narrow, flange-like ; basi- 



* Tbree special pa^rars, substantially the same, differing in some particnlars, vi?..: — 

 "On a new Oenns of Mexican Olirine Haminalia." < Ann. Mag. N. H. vii, 1841, pp. 521, 522. (The 



oriKiual notice ; genus 'lamed on p. 521 ; species D. phillipii, same page.) 

 " On a New Glirine Animal from Mexico.'' < Rep. Brit. Assoc. Adv. Soi. foi 1841, 1842, Trans, of the Scc- 



ons, p. 70. (8ii.;ie orthography of name.) 

 " On a ne>. Jlirine Animal from Mexico." < Araer. Jnuin, Sci. and Arts, xlil, 1^.2, pp. 334, 335. (Editorial 

 reprodnotion of the last ; name D. phillipsii on p. 335.) 

 I Special paper : — 

 "Macrocolns, cine ncuo Nagcruottiing ans dor Farnll'i der Springer." < Arcb. illr Natnrg., zwolfler 

 Jahrp;, Bd. i, 1846, pp. 1*2-17'^. (Speciee M. b..llicuB named, p. 176.) 



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