A New Pocket Gopher (Thomomys) and A New Spiny Pocket Mouse (Liomys) from Michoacan, Mexico by Eugene Raymond Hall

TITULO LARGO

A series of 17 pocket gophers of the species _Thomomys umbrinus_ obtained in 1943 from points 3, 4 and 5 miles south of Patzcuaro proves upon comparison to be an hitherto unrecognized subspecies which is described and named as follows:

#Thomomys umbrinus pullus#, new subspecies

_Type._ -- Male, adult, skin and skull; No. 100151, Univ. California Mus. Vert. Zool.; 5 mi. S Patzcuaro, 7800 ft., Michoacan, Mexico; March 10, 1943; obtained by Hubert H. Hall, original No. 117.

_Range._ -- Known only from 3 to 5 miles south of Patzcuaro, Michoacan.

_Diagnosis._ -- Size small (see measurements); color black or between Cinnamon-Brown and Snuff Brown; distal half of tail whitish and all of tail whitish in one specimen; lambdoidal crests perpendicular to sagittal plane of skull; posteroventral face of tympanic bulla rugose; jugal vertical (flat surface not oblique); interpterygoid space truncate at apex with sides curved outward (see figure).

_Comparison._ -- From topotypes of _Thomomys umbrinus supernus_ Nelson and Goldman, _pullus_ differs as follows: More individuals wholly black (except distal half of tail); underparts lacking white; rostrum broader; braincase anteriorly slightly more expanded dorsally; lambdoidal crests perpendicular to sagittal plane rather than inclined posteromediad; interparietal broader, [Male] 5.7 (5.0-7.0) versus 4.5, and in [Female] 6.5 (5.6-7.1) rather than 4.8 (4.4-5.1); flattened middle part of jugal vertical rather than oblique; in side view, mastoid and paroccipital processes farther apart thus exposing larger surface of mastoidal bulla; incisors, in both upper and lower jaws, slightly narrower; molariform teeth smaller, interpterygoid space truncate, at apex, with sides convex mediad, rather than V-shaped; ventral face of tympanic bullae rugose in posterior half rather than smooth.

_Remarks._ -- Among named subspecies of _Thomomys umbrinus_, _T. u. pullus_ most closely resembles _T. u. supernus_, the subspecies next adjacent to the northward. Therefore, the results of comparisons with only that subspecies are here reported upon. _T. u. tolucae_ to the eastward is for one thing a much larger animal and has slightly less procumbent upper incisors. So far as we know, _Thomomys umbrinus_ has not heretofore been reported from Michoacan. Of our seventeen skins, eight are brown, six are black and two are intermediate in color.

Most of these pocket gophers lived where there was a good growth of pine trees in the same areas where large pocket gophers of the species _Cratogeomys gymnurus_ occurred. The field notes of the collector of the type of _T. u. pullus_ record that when he was making a shallow excavation to reveal the gopher burrow in which he trapped the holotype, he found the burrow approximately five inches below the surface of the ground and that in digging deeper than was necessary he accidentally broke into the burrow of a _Cratogeomys_. Another member of our field party (E. R. Hall) when removing from its burrow a trapped _Thomomys_ that was caught only by the hind leg, dug around the animal whose burrow was approximately six inches underground and in doing so he also broke through the roof of a burrow of _Cratogeomys_. The burrow of _Cratogeomys_ was approximately sixteen inches below the ground.

Nowhere else, except 3 to 5 miles south of Patzcuaro, have the authors found two kinds of pocket gophers living together. The two-story arrangement south of Patzcuaro was possible because of the different levels at which the two kinds of animals made their burrows and the two-story arrangement was accidental and exceptional rather than the rule.

_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.