To confirm the presumed sexes of the two individuals under observation, both were collected while in copulation. Examination of the still-coupled specimens showed that both hemipenes of the male were everted and the left one had been inserted.
Apparently the pink-orange subcaudal patch of females is present only in the mating season. It was not present on specimens of this species taken by Raun and Wilks on Padre Island, Texas, in autumn, and it is not mentioned in taxonomic descriptions by Axtell (1954) and Smith (1946).
Measurements of adult specimens in our series indicate that females are of smaller average size than males, and, as previously noted by Smith (1946:132), females of this species have disproportionately shorter tails than do males (Table 1).
Holbrookia propinqua was previously collected on the barrier island by Axtell (1954:31; see also Axtell and Wasserman, 1953:2), who took specimens at Boca Jésus María, at a locality six to seven miles south of Boca Jésus María, and at a point 20 miles east-southeast of Matamoros. Axtell (loc. cit.) also lists specimens in the Museum of Zoology, University of Michigan, from Tepehuaje and from one mile north of Miramar Beach (Tampico).
Specimens (56): 3 ♂ ♂ adult, 1 ♂ subadult, 63433-436, Camp 1, July 7. 33 ♂ ♂ adult, 63437-440, 63443-445, 63447, 63448, 63450-456, 63458, 63460, 63462, 63463, 63465-468, 63470-478; 13 ♀ ♀ adult, 63441, 63446, 63449, 63457, 63459, 63469, 63479-485; 6 juv., 63442, 63461, 63464, 63486-488; Camp 2, July 9-July 10.
Table 1.—Measurements in Millimeters of Adult Specimens of Holbrookia propinqua from the Barrier Island of Tamaulipas
| Sex | Number of specimens | Snout-vent length | Tail length | Ratio: snout-vent to tail |
|---|---|---|---|---|
| Male | 33 | 56.0±0.5[A] (49-62) | 77.0±0.7 (69-85) | 0.731±0.001 (0.682-0.817) |
| Female | 14 | 50.9±0.5 (47-53) | 62.2±0.9 (57-68) | 0.825±0.001 (0.735-0.877) |
[A] Mean ± standard error; range indicated in parentheses.
Cnemidophorus gularis Baird and Girard: Whip-tailed Lizard.—At both camps we found this species in the same general habitat in which Holbrookia occurred, but in numbers decidedly fewer than the latter.
Specimens (4): 2 ♀ ♀ adult, 63489, 63490, Camp 1, July 7. 1 ♂ adult, 63491, 1 ♀ adult, 63492, Camp 2, July 9.