1915. Geomys personatus tropicalis Goldman, Proc. Biol. Soc. Washington, 28:134, June 29, type from Altamira, Tamaulipas.
Distribution in Tamaulipas.—Known only from vicinity of type locality, in southeastern part of state.
Geomys tropicalis was named as a subspecies of G. personatus in 1915 by E. A. Goldman. To my knowledge, no one other than Goldman has critically studied specimens of this pocket gopher, nor have specimens other than those listed in the original description been reported up to now. In 1953, Gerd H. Heinrich collected a series of 19 individuals one mile south of Altamira. These specimens were compared (by E. R. Hall in March, 1962) with the holotype and paratypes of G. p. tropicalis and were found to be indistinguishable.
Careful comparisons of the specimens from one mile south of Altamira with topotypes of G. personatus personatus (and specimens of other subspecies) indicate that tropicalis differs from personatus in a number of important characters, some of which tropicalis shares with Geomys arenarius of the Rio Grande Valley and adjacent areas in Texas, New Mexico, and Chihuahua (see Table 2).
Table 2.—Differences Between Three Species of Geomys.
| G. arenarius | G. personatus | G. tropicalis | |
|---|---|---|---|
| Zygomatic arches | parallel | narrower posteriorly | narrower posteriorly |
| Sagittal crest | absent | present | small |
| Squamosal knob | present | absent | present |
| Interparietal | subquadrant | triangular | triangular |
| Mesopterygoid fossa | V-shaped | U-shaped | V-shaped |
| Ratio, zygomatic breadth to basal length | 63.7-66.6 | 66.3-67.2 | 60.8-66.2 |
| Ratio, mastoid breadth to basal length | 58.0-60.4 | 59.8-63.1 | 58.0-59.6 |
| Border of premaxilla at incisive foramina | wedge-shaped | subquadrate | subquadrate |
As can be seen in the accompanying table tropicalis resembles arenarius in half of the eight characters considered, especially in the presence of a knob on the zygomatic process of the squamosal (the diagnostic character of arenarius according to Merriam, 1895:140) and in the shape of the mesopterygoid fossa. G. tropicalis differs from arenarius principally in having a low sagittal crest in adult males (lacking in arenarius) and in the shape of the interparietal bone, which in tropicalis is small (in some skulls difficult to see) and triangular instead of being relatively large and subquadrate as in arenarius.
G. tropicalis resembles personatus in half of the characters considered, notably in shape of the interparietal bone, outline of zygomatic arches, and constriction of the premaxillae where they border the incisive foramina.
Considering the distinctive combination of characters possessed by tropicalis, and its isolated, restricted geographic range (the nearest known record of Geomys is approximately 165 miles to the north), tropicalis is here regarded as a full species. A skull alone examined from 10 miles northwest of Tampico does not differ from those of other specimens studied.
The average weight of five non-pregnant July-taken females was 189.4 (180-200) grams. Weights of three males were 280, 270, and 255 grams. Females are in all measurements smaller than males.