. Bulletin. Natural history; Natuurlijke historie. PU 10251 YPM 16854. YPM 12563 Fig. 4. Diagrammatic drawings of middle Eocene isectolophid premolars showing range of varia- tion in development of P'' lingual cusps. All X 3. (YPM 16854 reversed.) Hypodigm: YPM 12563, 12901, 15297-15300, 16337, 16854; AMNH 11669-11671, 12132, 12221, 12222; USNM 22879-22881. Known distribution: Middle Eocene: Bridger B-D, Bridger formation, Bridger Basin, Wyoming. Diagnosis: Medium-sized isectolophids. Mean length Mi_3 = mm. P^ with one or two lingual cusps. See Table 2. Discussion: For almost fifty years
. Bulletin. Natural history; Natuurlijke historie. PU 10251 YPM 16854. YPM 12563 Fig. 4. Diagrammatic drawings of middle Eocene isectolophid premolars showing range of varia- tion in development of P'' lingual cusps. All X 3. (YPM 16854 reversed.) Hypodigm: YPM 12563, 12901, 15297-15300, 16337, 16854; AMNH 11669-11671, 12132, 12221, 12222; USNM 22879-22881. Known distribution: Middle Eocene: Bridger B-D, Bridger formation, Bridger Basin, Wyoming. Diagnosis: Medium-sized isectolophids. Mean length Mi_3 = mm. P^ with one or two lingual cusps. See Table 2. Discussion: For almost fifty years the type of /. latidens, PU 10251, was the only known specimen referable to that species. Then Troxell (1922a, p. 289) erected the species Homo- galax hridgerensis for an almost complete dentition (YPM 12563); in his comparisons he made no mention of /. latidens. The only subsequent mention of these species was a personal communication from H. E. Wood, quoted by Van Houten, (1945, p. 457, foot- note 68) which stated that H. hridgerensis was referable to /. latidens. Recent searching in many museum collections has uncovered several heretofore undescribed specimens of middle Eocene isectolophids, ranging from Bridger B through Bridger D (see hypodigm). Except for P^ all the dentitions are virtually identical. P'' is preserved in only 4 specimens (see fig. 4). In YPM 12563 (the type of H. hridger- ensis), from Bridger B-D, and in AMNH 12221, from Bridger D, P^ is triangular in outline and looks like a smaller replica of P*, with only a protocone lingually. A low protoloph ex- tends from the protocone towards the parastyle but is sharply terminated just before reach- ing the ectoloph. A lower metaloph extends towards die anterolingual corner of the meta-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Peabody M
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