464 



MONOGR. -xS OF NORTH AMERICAN EODENTIA. 



The Zapodidw mny be considered a connecting link (through Gerhillina ?) 

 Itctwcon tiie "central" or generalized structure which clinractcrizes the 

 Murida, and the "peripheral" or specialized type of structure which culmi- 

 nates in Dipodida. The family may l)e established upon the following com- 

 bination of characters, superimposed upon those that belong to the Myomorpli 

 series at large.* 



Chars.— Teeth, 18: I. ^; C.?^; Vm.\l\; M. |^. Superior incisors 

 compressed, sulcate; premolar small; molars rooted. Cervical vertebnc 

 unanchylosed (cf. Dipodida). Cranial portion of the skull shorter and broader 

 than in Murida: Auditory bullae transverse (cf. MuridcB), without special 

 development (cf. Dipodidce). Antcorbital foramen large, rounded (cf. typical 

 Murida), with a supplementary nick, or additional foramen, at its lower por- 

 tion. Malar mounting the zygomatic process of the maxillary to effect suture 

 with the lachrymal (cf. Muridtr). Zygomatic arch styloid, much depressed. 



* I bnvu but rnccutly received Mr. E. R. AUton'xconveuient' and valuable paper on the clugsiflcation 

 of tbe Rodeut8 (P. Z. S Jan. ltJT6, pp. (>1-9H, pi. iv), too late for snch use on I nbonld hnvo wiiibed to m.iko of 

 it iu tlie preparation of my nionu|rrapb of tho Murida; wliicb, though Btill (Dec. 1870) nDpnblisked, bos 

 been for Boine months in tbe metnl. 



Ill tbiH memoir, tho author arrnngeH Zapus (niulcr tho name of Jaculug) an one of three Hnbfamilieg 

 of Dipodida, which constitnto tho seventli and lust of liis oerieH of MyomorphH, Muridw being rnoged 

 third. Ill order to fully exhibit the grounda upon which he diffors with lue re8|iecting the position of 

 Zapus, — though our difference is chiefly in onr rceiicctive estimates of comparative degrees of inter-rela- 

 tionsbip and the taxonomio value of mntually conceded characters,— his diagnoses of Muridai, and of 

 Vipodidw, and its three assigned snbfamilies, are subjoined. 



"Family 111. MURin.G. Lower incisors compressed ; no premolars (except in Smintkinoi); molars 

 rooted or rootless, tuberoulate or with angular enamel-folds. Frontals contracted. Infraorbital opening 

 in typical forms high, per[>eudicular, wide above and narrowed below, with the lower root of the maxillary 

 zygomatic process more or less llattened into a perpendicular plate ; very rarely tho opening is either 

 large and oval or small and subtriaugulnr. Malar short and slender, generally reduced to a splint 

 between the maxillary and squamosal processes. External characters very variable. PoUex rudimentary, 

 but often with a small nail. Tail generally subiiaked and scaly, rarely densely haired. Cosmopolitan, 

 Ten subfamilies. * * *." 



" Famili/ Vll. DiPomD,E. Incisors compressed. Premolars present or abicnt. Qrinding-tcoth 

 rooted or rootless, not tuberculate, with more or fewer transverse euamel-folds. BkuU with the braiu- 

 case short and broad ; infraorbital opening rounded, very large (often as largo as the orbit) ; zygomntio 

 arch slender, curved downward ; the malar ascending in front to tho lachrymal in a lliittiMied periwii- 

 diuulur pinto; facial surface of tho uiaxillaries miuutely perforated ; mastoid portion of auditory bullie 

 usually greatly doreloped. Metatarsal bones greatly elongated, often fused into a cannon-bone. Form 

 gracilo ; front imrtion of body and fore limbs very small ; bind limbs long and strong, with from tbroo 

 to flvo digits; tail long, hairy. Three snbfamjiies :— 



"A. JacuHnw. One premolar above. Grinding-toeth looted. Cervical vertebra) free, mutatarsals 

 separate. Hind feet with five developed digits. Tail sparsely haired. Nearctio. [One genus,— ■/ochIiu.] 



" B, Dipodinai. Premolars present or abeent. Orinding-teeth rooted. Cervical vcrlobrie more or 

 less ankylosed. Metatarsals unitoil in a cannon-bone. Hind feet with only three digits functionally 

 developed. Tail thickly hairul, often tnftod. Palotarctic and Ethiopian. [Three geucra, — Dlpui, Atactaga, 

 rialycercomi/t. ] 



" 0. Pedclino!, One premolar above and lielow, Oriudiiig-toetb rootless. Cervical vertebra) free. 

 Metatarsals Heparalc. Hind feet with four well-doveluped digits, with short brood houf-like nulls. Tall 

 bushy throughout, not (ofted. Ethiopian." [One genus,— i'ldelei. I 





