Part 2

Dipodomys ordii parvabullatus new subspecies

Ord Kangaroo Rat

Type.--Male, adult, skull and skin, No. 35454, Mus. Nat. Hist. Univ. Kansas, from island, 88 miles south and 10 miles west of Matamoros, Tamaulipas, Mexico; obtained 19 March 1950 by E.R. Hall and Curt von Wedel; original No. 6778 E.R. Hall.

Range.--Islands along coast of Tamaulipas, Mexico.

Diagnosis.--Size small (see measurements). Color pale; entire dorsal surface Light Ochraceous-Buff (Capitalized color terms according to Ridgway: Color Standards and Color Nomenclature, Washington, D.C., 1912), purest on sides and flanks, upper parts lightly suffused with black; cheeks white; plantar surfaces of hind feet, dorsal and ventral stripe of tail, and anterior face of ear brownish. Skull small; auditory bullae smaller (actually and relative to remainder of skull) than in any other known kind of Dipodomys, excepting the one from Mustang Island, Texas (named beyond) in which the breadth is approximately the same; rostrum and interorbital region narrow.

Comparisons.--From Dipodomys ordii sennetti (Allen), of the mainland of Texas, D. o. parvabullatus differs in: Color paler on pigmented areas; white areas more extensive; skull smaller, in all parts measured, except the nasals which are slightly longer. From Dipodomys ordii compactus of Padre Island, Texas, D. o. parvabullatus differs in: Tail and hind foot shorter; skull smaller in all parts measured, especially so in breadth across maxillary processes of zygomatic arches.

Remarks.--D. o. parvabullatus resembles D. o. sennetti in external proportions and D. o. compactus in cranial proportions.

No difference was detected between specimens from the two sides of the tidal inlet 89 miles south of Matamoros. Only one of the 14 specimens is of the light color phase (upper parts Cartridge Buff). This pale specimen is from the north side of the inlet. The brownish stripe on the ventral side of the tail is absent on the distal two-fifths of the tail and the specimens are uniform in this respect. On the occlusal surfaces of the cheek-teeth, the enamel surrounding the dentine is incomplete on both the lingual and labial sides of the teeth of five individuals and is incomplete on the labial side of some of the teeth of a sixth specimen.

In the snap traps, all of which were baited with rolled oats, more than twice as many land crabs as kangaroo rats were taken. Judging from tracks in the sand, land crabs greatly outnumbered kangaroo rats. The parietal bones in two of the 13 skulls are much eroded by some parasite (seemingly nematode worms) and in one of these two specimens the roof of the left tympanic cavity is perforated. As regards life-zones, the occurrence of Dipodomys ordii in the lower part of the Lower Sonoran Life-zone on the off-shore beach 88 and 90 miles south of Matamoros is low zonally and perhaps is at or near the zonal margin of the range of the species. The crabs and worms conceivably are two of the environmental features inhospitable to the rats.

Specimens examined.--Total, 14, all from Tamaulipas, Mexico, as follows: 88 mi. S and 10 mi. W Matamoros, 7; 90 mi. S and 10 mi. W Matamoros, 7.

When Setzer (Univ. Kansas Publ., Mus. Nat. Hist., 1:473-573, December 27, 1949) reviewed the subspecies of Dipodomys ordii he lacked specimens of Dipodomys ordii compactus from the type locality or from anywhere else on Padre Island. He used as representative of D. o. compactus specimens from Mustang Island, Texas, the island next northeast of Padre Island. Through the courtesy of Mr. Stanley P. Young, Dr. Hartley H.T. Jackson and Miss Viola S. Schantz, of the United States Biological Surveys Collection, I have examined topotypes of D. o. compactus from Padre Island. This examination discloses that the kangaroo rats on Padre Island and Mustang Island are significantly different. Those from Mustang Island may be named and described as follows:

MEASUREMENTS (IN MILLIMETERS) OF ADULT MALES OF FOUR SUBSPECIES OF DIPODOMYS ORDII

Key: A Total length F Breadth across maxillary arches B Length of tail G Width of rostrum C Length of hind foot H Length of nasals D Greatest length of skull I Least interorbital width E Greatest breadth across bullae J Basilar length ----------------------------------------------------------------------

D. o. largus, type locality (K.U.)

A B C D E F G H I J Mean (9) 226 117 35.8 36.3 21.5 19.2 3.6 13.7 12.6 23.2 Maximum 241 128 37 37.2 22.0 19.9 3.7 14.2 13.9 23.9 Minimum 212 105 35 35.2 20.7 18.6 3.5 13.5 11.6 22.3 ----------------------------------------------------------------------

D. o. compactus, type locality (U.S.N.M.)

A B C D E F G H I J Mean (10) 230 126 37.7 36.6 22.1 20.0 3.8 14.0 12.5 23.8 Maximum 241 135 40 37.8 23.2 21.4 4.0 14.5 13.1 24.4 Minimum 208 118 35 35.5 21.6 19.2 3.6 13.1 11.3 23.1 ----------------------------------------------------------------------

D. o. parvabullatus, type locality and 2 mi. S of same (K.U.)

A B C D E F G H I J Mean (7) 216 111 35.9 36.4 21.7 19.6 3.6 13.8 12.1 23.0 Maximum 222 113 37 36.9 22.1 20.7 3.8 14.2 12.5 23.5 Minimum 210 109 34 35.9 21.3 19.1 3.3 13.4 11.6 22.1 ----------------------------------------------------------------------

D. o. sennetti, 2 mi. S Riviera, Texas (after Setzer, op. cit. :565)

A B C D E F G H I J Mean (5) 218 112 35.8 37.2 23.4 20.1 4.0 13.6 13.1 24.2 Maximum 222 115 38 38.2 24.1 20.7 4.3 14.4 13.2 24.6 Minimum 208 104 34 36.3 23.0 19.4 3.8 13.0 12.6 23.8 ----------------------------------------------------------------------

Dipodomys ordii largus new subspecies

Ord Kangaroo Rat

Type.--Female, adult, skull and skin, No. 27234, Mus. Nat. Hist., Univ. Kansas, from Mustang Island, 14 mi. SW Port Aransas, Aransas County, Texas; obtained 30 June 1948 by W.K. Clark; original No. 543.

Range.--Known from Mustang Island only.

Diagnosis.--Size medium (see measurements). Color pale, and as described for D. o. parvabullatus. Skull small; auditory bullae (actually and relative to remainder of skull) smaller than in any other known kind of Dipodomys, except D. o. parvabullatus in which breadth across bullae is approximately the same; notably narrow across maxillary processes of zygomatic arches.

Comparisons.--From Dipodomys ordii sennetti (J.A. Allen) of the mainland, D. o. largus differs in: Color paler on pigmented areas; white areas more extensive; skull averaging smaller except in basilar length and length of nasals which are approximately the same as in D. o. sennetti. From Dipodomys ordii compactus True of Padre Island, D. o. largus differs in: Body longer; tail shorter; skull narrower across tympanic bullae and across maxillary processes of zygomatic arches; nasals shorter. From Dipodomys ordii parvabullatus of the coastal island south of Padre Island, along the gulf coast of Tamaulipas, D. o. largus differs in: Body and tail longer; basilar length of skull averaging less; breadth across maxillary processes of zygomatic arches greater; premaxillae not extending so far behind nasals.

Remarks.--D. o. largus resembles D. o. compactus in external proportions and D. o. parvabullatus in cranial proportions. The degree of difference between D. o. compactus and D. o. largus is less than between D. o. compactus and D. o. parvabullatus. To me, the three subspecies mentioned in the preceding sentence are indistinguishable in color.