If 



12 MONOOUAl'US OF NOHTII AMKRICAN KODENTIA. 



un.l about lo appear as nn island of c.a.nd i.i tl.c dcnlinc area. This is 

 exactly what occurs in lIcq>eromi/ti, &c. 



Upon attentive eonsi.lerution of the sul)j.;ct. wo conclude that there is 

 really no es.sevtiul difference in the molar structure of our several f>eneru ; 

 that N,'ofo»ia and SIgmodon merely wear off their teclh faster than He.s- 

 peromi/s docs ; that the pattern just described for Neotomu is indicative of early 

 maturity; that with age the reentrant folds of enamel are ground off from 

 their connection with the general enveloping sheet, and appear as islands of 

 enamel in the general dentine area; and that, finally, these islands are rubbed 

 out, when we have, as a condition of senility, a continuous, depressed dentine 

 surface bounded by a raised, indented wall of enamel. 



We tabulate together a part of our skulls of the several species, both 

 real and nominal. The difference in the length of muzzle of the bushy- 

 tuiled species is evident from the figures. 



Table I.—Meaaaremeiitii of eighteen tkulh of varioiu «jicci«« of Neotoma 



No." 



;i44a 



Ui:\ 



80.M) 

 22U1 



nm 



a4(io 

 21G0 

 3,')97 

 ;i59d 

 ;i,VJ9 

 3()00 

 3G01 

 3602 



yoio 



Il>7() 



Locality. 



.a 



a 



Si 



3 



o 

 H 



South Atlantic St.ites.... 



do 



Saint Simon's, Ga 



do 



Soutbeiu States 



Geoi(!iii 



, do 



Sonora 



Fort T.'jon, Cttl .... 



do 



do 



do 



2.10 

 a. 0.-. 

 a.0o 



1.90 

 1,80 

 1.9S 

 l.(W 

 1.80 

 1.9o 

 1.87 



i.ei 



, do I 



, do 1 



Santa Clara, Cat 1 



Cliarco ICitcondido, Mox.. .' 

 W:ialiiii)!ton Territory....! 

 Deer Creek, "Nob", 



1.92 

 1.90 

 2.10 



2.10 

 2.05 



I 



0.72 

 0.70 

 0.68 

 0.65 



0.61 

 0.62 

 0. 62 



o.ns 



0.65 

 0.62 



° it 



1.08 

 1.05 

 1.02 



0.65 

 0.68 



0.98 

 0.84 

 0.97 

 1.02 

 0.94 

 0. 95 

 0.92 

 0.95 

 0.95 

 1.12 



1.07 

 1.05 



? 3 



0.27 

 0.25 

 0.25 

 0.25 

 0.82 

 0.24 

 0.21 

 0. 22 



o.2;t 



0.23 

 0.26 

 0.22 

 0.25 

 0.21 

 0.85 



11 



0.77 

 0.77 

 0.75 

 0.70 

 0.08 

 0.70 

 0.61 

 0. 65 

 0.76 

 0.72 

 0.71 

 0.70 

 0.75 

 0.70 

 0.77 



a is 



9 O 

 ►J ~ 



1.40 



0,20 

 0.25 



0.86 

 0.82 



1.30 

 1.25 

 1.20 

 1, 25 

 1.10 

 1.22 

 1.2.1 

 1.18 

 1.22 

 1.12 

 1.20 

 1.20 

 1.40 

 1.20 

 1.42 

 1.45 



Remarks. 



floriiana; iierfootly adult. 



do. 



floridana; mature. 



do. 



floridana; youngish. 

 floridana ; nearly adult. 

 floridana ; quite youug. 

 "niexioana"; mature. 



do. 



do. 



do. 



do. 



do. 



do. 



fatdpet ! adult, 

 "niieroiius"; adult, 

 "occidentalis"; udult. 

 cinerea; adult. 



\ti 



*Of the specimen, in the register of the National Museum, Smithsonian lustitution, and on its 

 label. The same with regard to the nnmbers in the first column of each table throughout the present 

 monograph. 



t Taken by laying the skull on a flat surface, and rocasnring perpendicularly from the surface to 

 the highest point of the parietals. The name mode of measurement in snhsequent tables. 



t From the tip of the incisors to the back of the condyle. The same, in following tables. 



N. 1).— Measurcmouts, throughout this article, are iu decimals of the Uuglish inch. 



