Produced by Chris Curnow, Joseph Cooper, Josephine Paolucci and the Online Distributed Proofreading Team at https://www.pgdp.net. A New Species of Heteromyid Rodent from the Middle Oligocene of Northeast Colorado with Remarks on the Skull BY EDWIN C. GALBREATH University of Kansas Publications Museum of Natural History Volume 1, No. 18, pp. 285-300, 2 plates August 16, 1948 University of Kansas LAWRENCE 1948 UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY Editors: E. Raymond Hall, Chairman; H. H. Lane, Edward H. Taylor Volume 1, No. 18, pp. 285-300, 2 plates August 16, 1948 UNIVERSITY OF KANSAS Lawrence, Kansas PRINTED BY FERD VOILAND, JR., STATE PRINTER TOPEKA, KANSAS 1948 [Illustration] 22-3342 [Transcriber's Note: Words surrounded by tildes, like ~this~ signifies words in bold. Words surrounded by underscores, like _this_, signifies words in italics.] [Illustration: PLATE 2. _Heliscomys tenuiceps._ Univ. Kans. Mus. Nat. Hist., Vert. Paleo. Coll. No. 7702. A, dorsal view; B, lateral view; C, ventral view. All views approximately × 5.] [Illustration: PLATE 3. _Heliscomys tenuiceps._ Univ. Kans. Mus. Nat. Hist., Vert. Paleo. Coll. No. 7702. A, lateral view of right side of skull showing structures in orbital area. ALS, alisphenoid. FR, frontal. MAX, maxillary. OS, orbitosphenoid. PAL, palatine. PC, presphenoid canal. SF, sphenoidal fissure. SFr, sphenofrontal foramen. SPal, sphenopalatine foramen. Approximately × 9.3; B, occlusal view of P4-M3. Approximately × 23.4.] A New Species of Heteromyid Rodent from the Middle Oligocene of Northeast Colorado with Remarks on the Skull By EDWIN C. GALBREATH Heretofore our knowledge of the osteology of _Heliscomys_ Cope has been extremely limited; this genus previously was known by its teeth, fragmental maxillaries, incomplete palatine bone and mandible, and part of one forelimb. In the summer of 1946 the writer, as a member of the University of Kansas Museum of Natural History field party, discovered the anterior part of a skull of _Heliscomys_ in the middle Oligocene deposits of Logan County, Colorado. This specimen, representing a new species, yields a welcome, and greatly desired addition to our fund of information about the genus. The writer is indebted to Dr. Robert W. Wilson for advice and helpful criticism in the course of this study, and to Mr. Bryan Patterson of the Chicago Natural History Museum for the loan of comparative material. Mrs. Bernita Mansfield of the Geology Department, University of Kansas, prepared the plates. Family HETEROMYIDAE ~Heliscomys tenuiceps~, new species _Holotype._--Anterior part of a skull with left P4-M3, No. 7702, Vertebrate Paleontological Collection, Museum of Natural History, University of Kansas. _Geological Age and locality._--Silts of Orellan age in the Cedar Creek facies of the Brule formation in "Chimney Canyon," Sec. 3, T. 11 N, R. 54 W, Logan County, Colorado.