The orange of males is most conspicuous in the pale postocular and postlabial areas; the stripes of the snout (distally) and the color of the neck at its juncture with the immaculate ventral surface are orange-yellow. The orange coloration is confined to males (all examined were sexually mature) and is probably not of seasonal occurrence (see comments under secondary sexual variation). I have not noticed this coloration in other males of the subspecies emoryi; however, long-preserved males might be expected to lack the orange color; the specimens mentioned above were initially preserved in alcohol. KU 51179 (plastral length 8.2 cm., from Ojinaga) is the smallest sexually mature male of the species spinifer that I have seen. Another character of note is the generally greater development of the plastral callosities (resembling muticus) than in other subspecies of spinifer or specimens of emoryi; three small adult males (KU 51177, 51990, 51987, plastral length 9.3, 9.9 and 9.1 cm., respectively) have large hyoplastral and hypoplastral callosities that appear to touch medially, and callosities on the epiplastron and both preplastra.
On July 8, 1953, an adult male of T. spinifer was removed from a hoop-net set in the Río Purificación at Padilla, Tamaulipas, México. I was particularly [513] impressed by the lack of whitish dots on the dark carapace; the following notes were taken from the freshly-killed specimen: carapace a uniform dark olive, lacking white dots and having a yellowish rim widest posteriorly; tubercles on anterior edge of carapace only slightly raised, inconspicuous; top of head olive with few dots and streaks; a well-defined yellowish postocular stripe not conspicuously interrupted; sharp contrast between dark olive on side of head and pale ventral coloration; yellowish-orange ventrolaterally on head; an uninterrupted slightly-curved line connecting the anterior margins of the orbits; carapace pear-shaped; underparts whitish, lacking markings. This specimen has since been destroyed. The only other specimen I have seen from this locality is a hatchling (UMMZ 69412, [Pl. 43]), which has a pale brownish or tan carapace that lacks whitish dots; it resembles emoryi in other characters. Although the absence of whitish dots is not distinctive, its combination with the uniform dark olive carapace in adult males and the fact that the Río Purificación is an isolated drainage system, suggests that soft-shelled turtles from that river system may warrant further taxonomic study.
Comparisons.—From all other subspecies of spinifer, T. s. emoryi can be distinguished by having a pale rim on the carapace that is four to five times wider posteriorly than it is laterally. This character, unique for emoryi, combined with patterns on the snout, side of head and carapace that are subject to little variation, permit ready identification of the subspecies emoryi. T. s. emoryi resembles pallidus, and guadalupensis and differs from spinifer, hartwegi and asper in having whitish tubercles or dots on the carapace. T. s. emoryi resembles guadalupensis but differs from pallidus, spinifer, hartwegi and asper in lacking conical tubercles along the anterior edge of the carapace on large females. For additional differences see accounts of other subspecies.
Some populations of T. s. emoryi resemble T. muticus in the size at which sexual maturity is attained and in the development of the plastral callosities. T. s. emoryi has a wide head that resembles that of T. ferox, T. ater, T. s. asper and T. s. guadalupensis; T. s. emoryi also resembles T. ferox and T. ater but differs from the other subspecies of T. spinifer and T. muticus in having a narrower carapace. T. s. emoryi resembles T. s. guadalupensis, T. s. pallidus and T. ater, and differs from the other subspecies of spinifer and T. muticus, in having the carapace widest farther posteriorly than one-half way back on the carapace. T. s. emoryi resembles T. ferox in having the shortest length of snout of the subspecies of spinifer. The plastron is shorter than in T. ferox, longer than in T. s. asper, and about the same length as in T. muticus and the other subspecies of T. spinifer.
Remarks.—Agassiz (1857, 1:407-08) did not designate a holotype in the original description of Aspidonectes emoryi; specimens are mentioned from the lower Río Grande of Texas, near Brownsville, and a stream of the Río Brazos drainage in Williamson County, Texas. The description is applicable to T. s. emoryi as herein restricted, except for the statement that the white tubercles of young specimens are "encircled by faint black lines"; that statement is presumably based on the juveniles from Williamson County. T. s. emoryi does not occur in Williamson County, Texas. Barbour and Loveridge (1929:225) listed MCZ 1909-10 and 1627 as cotypes. Stejneger (1944:65) mentioned MCZ 1909, 1913 and USNM 7855 as cotypes; the legend for Plate 20 (op. cit.) refers to a drawing that "corresponds fairly closely with the type (MCZ 1910) collected at Brownsville, Texas, by Col. Emory."
The syntypic series consists of seven specimens—MCZ 1627 (two specimens) from Williamson County, Texas; MCZ 1909 (three specimens) and 1910 from Brownsville, Texas; and USNM 7855 from Brownsville, Texas. The listing of number 1913 by Stejneger is considered a lapsus for 1910 as MCZ 1913 is catalogued as a Graptemys geographica (in letter dated November 17, 1959 from Dr. Ernest E. Williams). Stejneger's reference to MCZ 1910 as the type is considered unintentional and an inadequate designation of a lectotype.
In the "remarks" column of the USNM museum catalog, number 7855 is referred to as "Ag. Type." USNM 7855 is here designated as lectotype of Trionyx spinifer emoryi. The lectotype is a young specimen (female?) that is not easily sexed by external characters; the plastron measures (in centimeters) 6.3 in length, the carapace 8.2 in length and 7.0 in width, and the head 1.4 in width. The carapace is pale brown having inconspicuous whitish dots posteriorly and a pale rim that is approximately 6.8 times wider posteriorly (4.1 mm.) than it is laterally (0.6 mm.). The slightly curved dark line connecting the anterior margins of the orbits is dimmer than the dark lines that extend forward from the eyes. The pale postocular stripes having blackish, dotted borders are interrupted; there are no other markings on the side of the head. The ventral surface is immaculate except for a few dark dots on the right side of the carapace; the ground color is pale brown or tan, but the upper layer of skin can be scraped away revealing an underlying pale lavender-cream ground color. The tubercles along the anterior edge of the carapace resemble small rounded warts.
MCZ 1910 is an adult male T. s. emoryi having a plastron 10.7 centimeters in length. The carapace is pale brown having a relatively smooth anterior edge, inconspicuous whitish tubercles posteriorly, and a pale rim five times wider posteriorly than laterally; the pattern on the head resembles that of emoryi.
Each of three hatchlings of T. s. emoryi, 3.4, 3.5 and 3.9 centimeters in plastral length, bears an MCZ catalogue number of 1909. The carapaces are dark tan or gray having pale rims 3.7, 5.2 and 5.2 times wider posteriorly than laterally, and white dots absent or obscure posteriorly; two specimens have small blackish dots paralleling the pale rim posteriorly. The patterns on the heads are referable to emoryi.