55:25–26, May 12, 1942) that the californicus group should be divided into two groups (each group possibly amounting to something more than a species and something less than a subgenus) on the basis of a white rump and complex infolding of the enamel layer of the front of the first upper incisor versus a dark rump and simple infolding of the mentioned layer of enamel. He placed Lepus californicus merriami Mearns, among other subspecies, in a group different from the one in which he placed several other subspecies of Lepus californicus.

Specimens (skulls with accompanying skins) of the species Lepus californicus in the Biological Surveys Collection of the United States National Museum, representative of a gradual transition from the dark rump and simple fold in the enamel to the white rump and complex fold in the enamel are as follows: L. c. deserticola, No. 29733/41808, Paharanagat Valley, Nevada; Nos. 117463 and 156744, Beals Spring, Arizona. L. c. texianus, No. 24635/32031, Springerville, Arizona; No. 97453, Roswell, New Mexico; No. 118751, Toyah, Texas; No. 118749, Valentine, Texas; and No. 108700, Terlingua Creek, Texas. In the continuously distributed species Lepus californicus, along the northwest to southeast line provided by the localities of occurrence listed immediately above, there is a gradual transition from one kind of fold to the other kind and from one color of rump to the other color. It is clear that Shamel (op. cit.) was in error in his conclusions; the kinds of black-tailed jack rabbits to which Shamel (op. cit.) applied the name Macrotolagus should stand as given below.

Measurements (in millimeters) of adults of two subspecies of
Lepus californicus