Baiomys kolbi Hibbard, Trans. Kansas Acad. Sci., 55:201, June 18, 1952; Hibbard, Papers Mich. Acad. Sci., Arts and Letters, 38:403, April 27, 1953.
Type.—No. 24846, Univ. Michigan; right mandibular ramus bearing m1-m3 and incisor; Fox Canyon, upper Pliocene, Rexroad formation, Rexroad fauna, Univ. Michigan Locality K1-47, sec. 35, T. 34 S, R. 30 W, XI Ranch, Meade County, Kansas.
Referred material.—Univ. Michigan Nos. 24845-24848, 27494, 27497, 27499, 28566, 28861, 28878, 28880-28882, 28884, 28886.
Diagnosis.—Ramus of medium size to large for the genus; lower incisor short, narrow transversely, proödont; anterior median fold of m1 reduced or absent; cingular ridges of m1 and m2 moderately well-developed; m3 large relative to m1 and m2; average and extreme measurements of lower molars of seven specimens are, 3.0 (3.0-3.1).
Comparisons.—For comparisons with B. sawrockensis and B. rexroadi, see accounts of those species. From B. brachygnathus, B. kolbi differs in: molar row longer; m3 and jaw larger; diastema longer; masseteric ridge not so far forward; molars more depressed.
From B. minimus, B. kolbi differs in: molar row longer; m3 larger; jaw larger; diastema not so acutely curved; incisor shorter, narrower transversely, more proödont.
From B. musculus, B. kolbi differs in: anterior median fold of m1 slightly developed or absent, instead of well-developed; m3 larger (not reduced), external reëntrant valley broad and extending farther across crown of tooth; incisor smaller, and more proödont; cingular ridges of m1 and m2 less well-developed.
From B. taylori, B. kolbi differs in: molars larger, more depressed; incisor shorter, more proödont; m3 smaller relative to m1 and m2; external reëntrant valley of m3 broad, extending farther across crown of tooth.