MAMMALS OF THE MEXICAN BOUNDARY. 



887 



rate index to our knowledge of the steps in the evolution of recent 

 species. From this standpoint 1 have lately re-examined the members 



of what has been designated the " sonoriensis group," and have failed 

 to trace any connection between them and /'. la/copus, through inter 

 grading forms. 



On the contrary, comparison of series of specimens of P. leucopus 

 from Minnesota with the form nebrascensis occupying the adjacent 

 plains of Dakota, shows the two to be very distinct in both external 

 and cranial characters. Similar comparisons of specimens from Kan- 

 sas with those from Nebraska, and of series from Indian Territory 

 with series from Oklahoma, furnish no evidence of intergradation. 

 The series of P. leucopus from Minnesota to Indian Territory shows 

 but little geographical variation; while the campestrian forms on 

 the west show a wide range of variation. Indian Territory furnishes 

 nearly typical examples of P. leucopus; but these specimens from 

 Fort Cobb — are much more closely related to the P. Icxatnis than 

 to P. s. blandus from the same region. 



Remarks. — As in the case of blandus, this mouse prefers damp, 

 grassy places; but it appears to be more prolific. A specimen col- 

 lected at San Luis Springs (Lang's Ranch), September •'!, 1893, 

 contained 8 fetuses; another, taken at the head of Babacomeri 

 Creek, Arizona, October 19, 1893, contained 6; two from the Santa 

 Cruz River at Monument No. Ill (topotypes), October 1!). 1893, 

 contained 6 and 7; another from the same locality, October 23,1893, 

 contained 7. 



Record and measun merits of 56 Specimens of Peromyscus sonoriensis. 



Museum num- 

 ber. 



21241 



SSS i. . 



21171 



21169 

 21240 

 20603 

 20608 



20602 



20604 

 20599 

 20598 



20600 



J 3 



3. ■& 



37240 2067 



21237 37239 2076 



22243 Alcoholic. 2081 



....do.... 2082 



36138 2134 



16136 'i 18 



36158 2162 



35763 762 



35768 763 



35762 769 



35764 770 

 35759 772 

 35758 77:: 



771 

 775 



Li i>m in j . 



San Bernardino Ranch a1 Monu- 

 ment No. 77. 



.do. 

 .do. 

 .do. 



Date. 



San Pedro 

 No. 98. 



....do 



....do 



....do 



....do 



Kiver. Monument 



ria, near Monument No. 

 Ill, on Santa Cruz River (camp 

 jusl soul b of Mexico line >. 



....do 



....do 



....do 



....do 



....do 



IS! I'. 1 



Aug. 21 



Aug. 27 

 Aug. 31 

 Ocl 6 

 Oct. 16 



Oct 21 

 Oct. 26 

 N.OV. 2 

 . do 

 Nov. 8 



.do... 



.do... 

 .do... 

 .do... 

 .do... 



Se\. 



' juv. 



' im. 

 ' im. 

 $ad. 



' ad. 

 ' juv. 

 - ad. 



' im. 

 9 ad. 



'■ 

 f ad. 



' im. 



in in . 

 153 



160 65 

 165 



114 

 172 



117 



171 



162 

 157 



111 



176 SO 



165 69 



L37 60 



m m . 

 20.0 



21.0 



22.0 



22.0 

 19.5 

 21.5 

 19.5 

 20.0 



It 

 14.5 



13.0 

 16.5 

 15.0 

 14.0 



20.5 15.5 

 21.0 15.0 

 19.5 11..". 

 21.0 15. 5 



14.0 



