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Key to the Reithrodontomys of the USA

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This key to the harvest mice (Reithrodontomys) of the United States is borrowed from Spencer & Cameron (1982).

Spencer SR, Cameron GN. 1982. Reithrodontomys fulvescens. Mammalian species (174): 1-7.

1

  • First primary fold of M3 at least as long as second primary fold, each usually extending more than halfway across crown; worn occlusal surface of left m3 S-shaped.... Reithrodontomys fulvescens
  • First primary fold of M3 distinctly shorter than second primary fold, extending less than halfway across crown; worn occlusal surface of left m3 C-shaped . . . . . 2


2

Return to couplet #1

  • Distinct labial ridge, often with cusplets, on m1 and m2; major fold and 2nd primary fold in M1 and M2 tending to coalesce, isolating anterior cusps from posterior cusps; occurring in southeastern USA... Reithrodontomys humulis
  • No distinct labial ridge on m1 and m2; major fold and second primary fold in M1 and M2 meeting but not coalescing, and thus isolating anterior cusps from posterior cusps; not occurring in southeastern USA . . . . . 3


3

Return to couplet #2

  • Breadth of braincase not exceeding 9.6; rostrum short and broad; tail shorter than head and body; occurring in Great Plains and southwestern USA.... Reithrodontomys montanus
  • Breadth of braincase more than 9.5; rostrum longer and narrower; tail approximately equal to, or longer than head and body . . . . . 4


4

Return to couplet #3

  • Fur of upperparts long, dense, heavily pigmented; ears blackish; occurring in salt marshes in vicinity of San Francisco Bay, California... Reithrodontomys raviventris
  • Fur of upperparts shorter and less dense, varying from pale buff to reddish brown; ears buffy or fuscous; not occurring in salt marshes in vicinity of San Francisco Bay, California... Reithrodontomys megalotis
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