MAMMALS OF THE MEXICAN BOUNDARl, 



387 



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

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

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

 to trace any connection between them and P. leucopus, 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 w est 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. texanus than 

 to P. s. blandus from the same region. 



Remarhs. — 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 3, 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 19, 1893, 

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

 contained 7. 



Record and measurements of 56 Specimens of Peromyscus sonoriensis. 



Museum num- 

 ber. 



21241 



21237 

 22243 

 22255 

 21171 



21169 

 21240 

 20603 

 20608 

 20602 



20604 

 20599 

 20598 

 20600 

 20605 



37240 



37239 

 Alcoholic. 

 ....do.... 



36138 



35764 

 35759 

 35758 

 35760 

 35765 



2067 



2076 

 2081 

 2082 

 2134 



36136 2138 

 36158 : 2162 

 35763 ' 762 

 35768 763 

 35762 769 



770 



772 

 773 

 774 

 775 



Locality. 



San Bernardino Ranch at Monu- 

 ment No. 77. 



.do. 

 .do. 

 .do. 



San Pedro 

 No. 98. . 



River, Monument 



Date. 



....do 



....do 



....do 



....do r. 



La Noria, near Monument No. 

 HI, on Santa Cruz River (camp 

 just south of Mexico line). 



....do 



....do 



....do 



..;.do 



....do 



1892 

 Aug. 21 



Aug. 27 

 Aug. 31 

 Oct. 6 

 Oct. 16 



Oct. 21 

 Oct. 26 



Nov. 2 

 ...do.. 

 Nov. 8 



.do., 

 .do., 

 .do., 

 .do., 

 .do.. 



J juv. 

 cf im. 

 cf im. 

 9 ad. 



cf ad. 

 d' juv. 

 cf ad. 

 dim. 

 9 ad. 



cf. 



d'ad. 

 ? im. 

 ? im. 



-f im. 



mm. 

 153 



160 

 165 



165 

 144 

 172 

 147 

 171 



162 

 157 

 144 

 153 

 137 



mm. 

 20.0 



21.0 

 22.0 



22.0 

 19.5 

 21.5 

 19.5 

 20.0 



20.5 

 2L0 

 19.5 

 21.0 

 20.5 



14 

 14.5 



15.0 

 13.0 

 16.5 

 15.0 

 14.0 



15.5 

 15.0 

 14.5 

 16.5 

 14.0 



