_Measurements._--Average and extreme measurements of five adults of each sex, are as follows: Total length, male 184 (178-198), female 185 (174-194); length of tail, 54 (48-60), 53 (47-57); length of hind foot, 26.8 (25-29), 27.6 (26-29); weight, 86.1 (78.7-96.9), 74.3 (70.2-84.8) grams; basilar length, 30.2 (28.8-31.3), 28.6 (27.8-29.1); zygomatic breadth, 23.2 (22.3-24.6), 21.3 (20.8-21.8); least interorbital breadth, 5.9 (5.8-6.1), 6.4 (6.0-6.8); mastoid breadth, 17.8 (17.1-18.7), 17.2 (16.6-17.5); length of nasals, 12.4 (11.8-13.0), 11.5 (11.0-12.5); breadth of rostrum, 7.5 (6.9-8.2), 7.1 (6.9-7.3); length of rostrum, 14.1 (13.4-14.5), 13.3 (12.7-13.5); alveolar length of maxillary tooth-row, 7.0 (6.7-7.5), 6.9 (6.8-7.0); palato-frontal depth, 13.2 (13.0-13.4), 12.9 (12.3-13.5). _Specimens examined._--Total, 17, all from 7800 ft., Michoacan, as follows: 3 mi. S Patzcuaro, 1; 4 mi. S Patzcuaro, 10; 5 mi. S Patzcuaro, 6. * * * * * In 1943 a series of fifteen spiny pocket mice, _Liomys irroratus_, was obtained within a radius of five miles of Patzcuaro and, mostly on geographic considerations, the animals were assigned to _Liomys irroratus alleni_ (Coues). In fact, in his "Revision of the Spiny Pocket Mice," Goldman (N. Amer. Fauna, 34:57, 1911) had thus identified the one specimen available to him from Patzcuaro. Critical examination of the series, however, revealed cranial features not described in the named kinds from adjoining geographic areas, and comparisons showed that the animal from Patzcuaro differs subspecifically from any named kind. The new subspecies may be known as: #Liomys irroratus acutus#, new subspecies _Type._--Female, adult, skin and skull; No. 100171, Univ. California Mus. Vert. Zool.; 2 mi. W. Patzcuaro, 7700 ft., Michoacan, Mexico; March 10, 1943; obtained by E. R. Hall and J. R. Alcorn, original No. 3837 of Alcorn. _Range._--Known only from the vicinity of Patzcuaro, Michoacan. _Diagnosis._--Size large (see measurements); upper parts dark brown; posterior border of nasals V-shaped with apex directed anteriorly; frontomaxillary suture medially concave or rarely straight; interparietal subcircular; basisphenoid wide; tympanic bullae large.