Chapter V: Part 5

BAJA CALIFORNIA: Colorado River delta, 7 mi. E Cerro Prieto; Imperial Irrigation District, Alamo Canal, 15 mi. S Internat'l Boundary and Salfatana Canal, 1 mi. N Black Butte (Linsdale and Gressitt, 1937:222).

COAHUILA: San Juan (Schmidt and Owens, 1944:103).

Hitherto, soft-shelled turtles of the species _Trionyx spinifer_ from the southern and southwestern United States having a pattern of white dots on the carapace have been relegated to the subspecies _emoryi_, but my examination of soft-shelled turtles from Texas has indicated that _T. s. emoryi_ as previously conceived, is a composite of three subspecies. It is necessary, therefore, to recognize two new subspecies.

=Trionyx spinifer guadalupensis= new subspecies

Guadalupe Spiny Softshell

Plates 41 and 42

_Holotype._--UMMZ 89926, alcoholic adult male; obtained 15 miles northeast Tilden, McMullen County, Texas (Pl. 41, bottom, left).

_Paratypes._--Forty-two specimens: ANSP 16717 (hatchling), no data; USNM 78515-16 (hatchlings), Colleto Creek, Victoria County, Texas; TU 10143-45, 10148, 10150-59, 10161-65 (adult males), TU 10176, 10833 (immature males), TU 10147, 10149, 10155 (immature females), TU 10160 (adult female), Guadalupe River, 9 miles southeast Kerrville, Kerr County, Texas; UMMZ 89915-21, 89924-27 (adult males), UMMZ 89922-23 (immature females), same locality as holotype; UMMZ 92752 (immature female), San Antonio River, 3 miles west-northwest Goliad, Victoria County, Texas.

_Description of holotype._--Carapace nearly circular, widest at level of posterior border of hypoplastra; margin entire; dorsal surface "sandpapery" to touch; pale rim separated from ground color of carapace by well-defined, blackish line that is wavy and narrowly interrupted posteriorly and anteriorly; pale rim approximately 1.8 times wider posteriorly (5.4 mm.) than laterally (3.0 mm.); pale rim increasingly narrower anteriorly, absent in nuchal region; tubercles in nuchal region low, scarcely elevated, lacking sharp tips; ground color of carapace olive having pattern of whitish spots and small tubercles; most whitish tubercles inconspicuous pinpoints; other small tubercles in center of whitish spots, mostly approximately 2 millimeters in diameter; largest white spot 3.4 millimeters in diameter; most white spots surrounded by blackish ocelli or parts thereof; whitish spots distributed over entire surface of carapace; certain features of bony carapace evident through overlying skin; carapace highest in region of second and third neurals, forming obtuse, gently sloping, vertebral, keel; undersurface of carapace butterscotch yellow, lacking markings; maximum length, 16.5 centimeters; greatest width, 13.5 centimeters.

Plastral surface butterscotch yellow, lacking markings, extending slightly farther forward than carapace; anterior and posterior lobes rounded; anterior lobe slightly truncate; certain features of bony elements of plastron visible through overlying skin; maximum length of plastron, 12.0 centimeters.

Head, extended to posterior level of eyes, terminating in flexible snout; septal ridges projecting into each rounded nostril; jaws closed, each covered by fleshy lips except anteriorly where horny portions exposed; dark triangular mark in front of eyes, base line connecting anterior margins of orbits forming series of dots; pale stripes extending forward from eyes having faint inner, blackish borders; eyelids partly open having blackish dots; pale subocular blotch on right side of head having border of black dots.

Forefeet and hind feet well-webbed having five digits each; each limb having nails on first three digits; each forelimb with four antebrachial scales, three of these having free edge; each hind limb with two horny scales, one smooth on posterodorsal surface and other with free edge on posteroventral surface; pattern toward insertion of forelimbs indistinct.

Tail terminating in flexible point; penis exposed; cloacal opening extending beyond posterior edge of carapace; tail olive above bordered by blackish marks; few black dots laterally on left side.

Undersurface of soft parts of body buff, lacking markings; few dark marks posteriorly on webbing of limbs, encroaching on soles and palms.

_Range._--Southcentral Texas in the drainage systems of the Nueces and Guadalupe-San Antonio rivers; the Colorado River drainage in Texas is inhabited by a population that more closely resembles _guadalupensis_ than _pallidus_. See comments under subsection entitled "Remarks" and Fig. 19.

_Diagnosis._--Juvenal pattern of white dots that are conspicuous on anterior half of carapace, and usually as large as those on posterior half; white dots, sometimes 3 millimeters in diameter, encircled with blackish ocelli in adult males.

_Description._--Plastral length of smallest hatchling, 3.3 centimeters (ANSP 16717); of largest male, 13.5 centimeters (TU 10162); of largest female, 22.0 centimeters (TU 10160).

Hatchlings having white dots on anterior half of carapace; white dots anteriorly nearly as large as those posteriorly, encircled with blackish ocelli, and conspicuous on dark background (ANSP 16717, Pl. 41; USNM 78515-16; Stebbins, 1954:181, Pl. 26B), or smaller than those posteriorly, not encircled with dusky ocelli, and inconspicuous on pale background (TNHC 1446); pale rim of carapace less than four times as wide posteriorly as laterally.

Adult males resembling holotype; size of white tubercles on carapace variable; most, if not all, tubercles surrounded by narrow blackish ocelli, or parts thereof; largest white tubercles or dots in most specimens exceeding one millimeter and in some specimens three millimeters in diameter (TU 10163); white dots often slightly elongate (UMMZ 89917, 89920, 89926; TU 10152, 10145); juvenal pattern of white dots seemingly more contrasting in _guadalupensis_, owing to dark ground color of carapace, than in _pallidus_ or _emoryi_ that have pale brown or tan carapaces; small tubercles along anterior edge of carapace rounded, obtuse, wartlike, never conical; sharp tips often lacking (TU 10153).

Large females often having whitish spots on anterior half of carapace (TU 10160, Pl. 42, upper, right; 10142); carapace dark having ill-defined mottled and blotched pattern; tubercles along anterior edge of carapace low, rounded, rarely equilateral, never conical; small blackish dots rarely on surface of carapace (UMMZ 89923).

Pattern on side of head and snout of little diagnostic value; postocular stripe usually interrupted, but configuration variable, consisting of pale anterior, dark-bordered segment (just behind eye); posterior segment of postocular stripe usually less well-defined and generally blending with adjacent ground color; pale postocular stripe sometimes uninterrupted and dark-bordered throughout its length (TU 10157, 10159, 10176); pattern on dorsal surface of snout variable; pattern usually consisting of uninterrupted dark line (slightly curved anteriorly) connecting anterior margins of orbits (TU 10161, 10164, 10159, 10143), or dark line interrupted (TU 10153, 10154, 10176), absent (TU 10163), or present in addition to dark inner borders of pale stripes that extend anteriorly from eyes (TU 10149, 10162); small, often fine, dark markings, on dorsal surface of limbs, especially forelimbs; ventral surface of plastron and soft parts of body usually whitish, lacking markings; small blackish spots occasionally in region of bridge (TU 10149); dark marks occurring on webbing of limbs and often encroaching on soles and palms.

Ontogenetic variation in PL/HW, mean PL/HW of specimens having plastral lengths 7.0 centimeters or less, 3.83, and exceeding 7.0 centimeters, 5.18; ontogenetic variation in CL/CW, mean CL/CW of specimens having plastron lengths 8.5 centimeters or less, 1.14, and exceeding 8.5 centimeters, 1.22; mean CL/PCW, 2.11; mean HW/SL, 1.38 (including subspecies _pallidus_); mean CL/PL, 1.37.

_Variation._--Two hatchlings (ANSP 13447, Bexar County; TNHC 1446, McMullen County) more closely resemble _pallidus_ than _guadalupensis_.

Some individuals from the Colorado River drainage have features suggesting those that are characteristic of _pallidus_. Large females have obtuse, knoblike somewhat triangular-shaped tubercles along the anterior edge of the carapace, which are never conelike (TU 14439-40, 10187, 16036.1; BCB 6010). The tubercles along the anterior edge of the carapace are more elevated than in turtles from drainage systems west of the Colorado. Whitish spots are usually absent anteriorly on the carapace, but may be evident through the mottled pattern of large females (BCB 6010, plastral length, 19.7 cm.). The pale postocular stripe is usually interrupted, whereas the dark line connecting the anterior margins of the orbits is usually not interrupted; the two characters last mentioned show alliance with _guadalupensis_.

The carapace of hatchlings from the Colorado River is pale having whitish dots, smaller anteriorly than posteriorly, which may be encircled with dusky ocelli (TNHC 20257) or not (ANSP 11889, BCB 5055, SM 3282). Many hatchlings are not distinguishable from _pallidus_ (TCWC 7262, TNHC 4975, SM 4924, 6106). I have not seen hatchlings from the Colorado River that resemble ANSP 16717.

The pattern on the carapace of adult males from the Colorado River drainage resembles that of _guadalupensis_ (Pl. 41, bottom, right) but the whitish dots are usually smaller and may not be encircled with blackish ocelli (BCB 4066, TU 14485). An adult male (TU 14476) from the South Fork of the Llano River has whitish dots three millimeters in diameter and encircled with blackish ocelli (_guadalupensis_), whereas another adult male (USNM 83690) from a tributary of the Colorado, the South Concho River, resembles _pallidus_.

Eight specimens from the San Saba River (TU 14419 [6 specimens], 14439-40), that range in plastral length from 6.8 to 17.0 centimeters are impressive because of the dark brownish coloration on the carapace. The smallest individual, which is also the only male in the series, is paler. The mottled and blotched pattern on the females is therefore not contrasting; the largest females have elevated whitish prominences in the center of the carapace posteriorly. An immature male (UMMZ 70348) from the South Concho River also has a dark brown carapace, and lacks white dots. The dark coloration of the carapace of these specimens recalls the TU series of _T. s. emoryi_ from the Pecos River, Terrell County, Texas.

Color notes taken from a freshly-killed adult female from the Llano River, two miles west Llano (TU 16036.1, Pl. 42), are: pattern on carapace of dark olive or blackish marks that form an irregular reticulum or marbling on a paler background that varies from brownish to buff and has an orange or reddish tinge in some areas; small whitish spots posteriorly; pale rim yellowish, evident only at sides of carapace; dorsal surface of soft parts of body olive-green, becoming paler with yellowish tinge toward insertions of limbs and neck; no contrasting pattern on limbs or neck and head; yellowish on sides of body; ventral surface whitish lacking dark marks, yellowish at region of bridge, axillary region and on neck; chin olive-yellow.

_Comparisons._--_T. s. guadalupensis_ can be distinguished from all other subspecies of _T. spinifer_ in having: (1) large white dots, sometimes three millimeters in diameter, on a dark background usually surrounded with blackish ocelli and conspicuous on the anterior half of the carapace (some as large as those on posterior half) in adult males, and (2) whitish dots on the anterior half of the carapace, in hatchlings, that are often encircled with dark ocelli. _T. s. guadalupensis_ resembles _pallidus_ and _emoryi_ in having white tubercles or dots on the carapace and therein differs from _spinifer_, _hartwegi_ and _asper_. _T. s. guadalupensis_ resembles _pallidus_ but differs from _emoryi_ in having a pale rim that is less than four times wider posteriorly than laterally. _T. s. guadalupensis_ resembles _emoryi_ but differs from _pallidus_, _spinifer_, _hartwegi_ and _asper_ in having along the anterior edge of the carapace tubercles that are flattened or wartlike prominences often lacking sharp tips in adult males; these tubercles are never conical in large females.

_T. s. guadalupensis_ has a wide head, a feature shared with the subspecies _asper_ and _emoryi_, but differs from _emoryi_ in having a wider carapace. _T. s. guadalupensis_ resembles _emoryi_ and _pallidus_ but differs from the other subspecies in having the carapace widest farther posterior than one-half the length of the carapace. The length of snout in _pallidus_ and _guadalupensis_ is shorter than in _spinifer_ and _hartwegi_ but is longer than in _emoryi_. _T. s. guadalupensis_ differs from _asper_ but resembles the other subspecies in having a relatively long plastron.

_Remarks._--Some individuals of _guadalupensis_ have characteristics that are applicable to _emoryi_. TNHC 12352 (Llano River) a hatchling, has conspicuous white dots confined to the posterior third of the carapace; the pale rim, however, is not widened posteriorly. TU 10156 (Guadalupe River) has a conspicuously widened pale rim on the carapace that is approximately 3.4 times wider posteriorly (8.5 mm.) than laterally (2.5 mm.).

_T. s. guadalupensis_ more closely resembles _pallidus_ than _emoryi_. Turtles living in rivers that drain into the Gulf of Mexico east of the Guadalupe-San Antonio river system successively show increasing resemblance to _pallidus_ from west to east.

The expression of intergradation between _guadalupensis_ and _pallidus_ is of a clinal nature that involves parallel changes in the pattern on the snout, side of head, limbs (to a lesser degree), tuberculation along the anterior edge of the carapace, size of whitish tubercles or dots, and the distinctness of the blackish ocelli that surround the whitish dots on the carapace. These characters form a well-marked gradation or cline that extends over a considerable area. There is, however, no continuous environmental gradient because the populations are relatively isolated by occupying adjacent drainage systems. The sharpest break in the gradation of characters mentioned above occurs between the Colorado River and Brazos River drainages. The population of softshells in the Colorado River drainage is actually an intergradient one, but more closely resembles _guadalupensis_, whereas the population in the Brazos River drainage more closely resembles _pallidus_. For convenience the turtles inhabiting the Colorado River drainage are referred to _guadalupensis_ and those in the Brazos River drainage to _pallidus_. Some individuals from farther west than the Colorado River drainage will resemble _pallidus_, and a few individuals from father east than the Brazos River drainage will resemble _guadalupensis_.

The gradation of some of the characters mentioned above terminates in the subspecies _emoryi_. It, however, has characters not found in _pallidus_ or _guadalupensis_, and is more distinct from either of those subspecies than either is from each other; the difference in characters as well as the break in the gradient of characters between _guadalupensis_ in the Nueces River drainage and _emoryi_ in the Río Grande drainage is greater than that between _guadalupensis_ in the Colorado and _pallidus_ in the Brazos River drainages.

I have refrained from designating individuals between these three subspecies (_emoryi_, _guadalupensis_ and _pallidus_) as "intergrades" on the distribution maps, and only mention (in text) those individuals whose characters show a decided tendency toward the adjacent subspecies. For further comments on intergradation see the account of _T. s. pallidus_.

_Specimens examined._--Total 97, as follows: TEXAS: _Bandera_: KU 50834, Hondo Creek, 4 mi. W Bandera; TNHC 797-98, 7 mi. SW Medina. _Bexar_: ANSP 13447, Helotes; MCZ 4587; USNM 10789, 71009, San Antonio. _Borden_: BCB 4066, 7 mi. N Vincent. _Brown_: TNHC 7262, 1 mi. E Brownwood. _Comal_: USNM 7700, New Braunfels. _Dawson_: TNHC 21594-95, 10 mi. E Lamesa. _Frio_: USNM 7747, Río Seco. _Gillespie_: TU 10185, 10187, 10205, Beaver Creek, "near" Doss. _Hays_: AMNH 29950-52, San Marcos. _Kerr_: SM 2553, headwaters Turtle Creek; TU 10142-45, 10147-65, 10176, 10833, Guadalupe River, 9 mi. SE Kerrville. _Kimble_: BCB 5052-55, 6010, 3 mi. SE Telegraph; TU 14476, South Fork Llano River, 1.5 mi. SE Telegraph; TU 14485, Llano River, 10 mi. W Junction. _Lavaca_: SM 2554-55, 2559, 3 mi. NNE Hope. _Llano_: TNHC 12352, TU 16036 (2), Llano River, 2 mi. W Llano. _McMullen_: TNHC 1446, 10 mi. W Simmons, Live Oak County; UMMZ 89915-27, 15 mi. NE Tilden. _Matagorda_: ANSP 11889, Matagorda. _San Saba_: SM 6106; TU 14419 (6), 14439-40, San Saba River, 11 mi. NNW San Saba. _Tom Green_: SM 3282, UMMZ 70348, USNM 83690, South Concho River at Christoval. _Travis_: SM 659-60, 8.5 mi. from mouth of Onion Creek in Colorado River near Austin; SM 4924, Onion Creek; TNHC 4975, Upper Bull Creek; TNHC 20257, Marshall Ford Dam. _Victoria_: CM 3118, Black Bayou; UMMZ 92752, San Antonio River, 3 mi. WSW Goliad; USNM 78515-17, Colleto Creek, Guadalupe River. _County unknown_: ANSP 16717; TNHC 1404.

_Records in the literature._--TEXAS: _Bandera_: 24 mi. WNW Medina (Brown, 1950:250). _Burnet_: Colorado River (Strecker, 1909:8). _Gillespie_: 20 mi. N Harper (Brown, _loc. cit._). _Kendall_: Cibolo Creek at Boerne (Strecker, 1926:8). _Kerr_: Guadalupe River, 3 mi. above Kerrville (TCWC 474, listed in card file). _Mason_: 12 mi. NE Mason (TCWC 3303, listed in card file). _Matagorda_: Bay City (Brown, _loc. cit._). _Real_: (Stejneger, 1944:66). _Wilson_: Cibolo River, 30 or 40 mi. N Sutherland Springs (Strecker, 1935:23).

=Trionyx spinifer pallidus= new subspecies

Pallid Spiny Softshell

Plates 39 and 40

_Holotype._--TU 484, alcoholic adult male; obtained from Lake Caddo, Caddo Parish, Louisiana on June 27, 1947, by Fred R. Cagle and party (Pl. 39, lower, left).

_Paratypes._--Forty-two specimens: TU 481, 490, 678 (hatchlings), TU 381, 472, 488 (immature males), TU 475, 478, 486, 1232, 1291, 10170 (adult males), TU 399, 487 (immature females), TU 469 (adult female), Caddo Lake, Caddo Parish, Louisiana; TU 15818 (immature male), TU 15819 (adult male), Cross Lake, Caddo Parish, Louisiana; TU 1253, 13211 (adult males), TU 13266 (immature female), Sabine River, 8 miles southwest Merryville, Beauregard Parish, Louisiana; TU 13281-82 (adult males), TU 13280, 13265 (immature females), TU 13303-04, 13306 (adult females), Sabine River, 8 miles southwest Negreet, Sabine Parish, Louisiana; SM 2375 (adult male), Wallace Bayou, De Soto Parish, Louisiana; TU 1122 (adult male), Lacassine Refuge, Louisiana; UMMZ 92754 (adult male), 5 miles west Iowa, Calcasieu Parish, Louisiana; KU 40174-76, OU 27297 (adult males), OU 27290 (immature female), Lake Texoma, 2 mi. E Willis, Marshall County, Oklahoma; KU 50832 (hatchling), mouth of Caney Creek, 4 miles southwest Kingston, Marshall County, Oklahoma; CNHM 15474 (immature female), Kiowa County, Oklahoma; KU 2966-67 (immature females), KU 2934, 2947 (adult males), KU 2973 (adult female) Lewisville, Lafayette County, Arkansas.

_Description of holotype._--Carapace circular, widest at level of posterior edge of hyoplastra; margin entire; dorsal surface "sandpapery" to touch; pale rim separated from ground color of carapace by well-defined, slightly ragged, blackish line; pale rim approximately 2.1 times wider posteriorly (4.7 mm.) than it is laterally (2.2 mm.); pale rim increasingly narrower anteriorly, absent in nuchal region; tubercles along anterior edge of carapace triangular with sharp tips becoming flattened and inconspicuous at level of insertions of arms; ground color of carapace brownish having pattern of small whitish tubercles; most whitish tubercles inconspicuous, of pinpoint size, giving surface of carapace "sandpapery" effect; largest white tubercles posteriorly, approximately 1.2 millimeters in diameter; whitish tubercles smaller anteriorly, largest approximately 0.6 millimeters in diameter; whitish tubercles tend to form two parallel lines coincident with longitudinal sutures of neurals posteriorly in center of carapace; certain features of bony carapace evident through overlying skin; carapace highest in region of third and fourth neurals, forming obtuse, gently sloping, vertebral keel; undersurface of rear margin of carapace whitish having pinkish tinge and no markings; maximum length, 16.8 centimeters; greatest width, 14.3 centimeters.

Plastral surface extending slightly farther forward than carapace, whitish having pinkish tinge and no dark markings; anterior and posterior lobes rounded, posterior lobe more acutely; certain features of bony elements of plastron visible through overlying skin; maximum length, 12.2 centimeters.

Head extended, terminating in flexible snout; septal ridges projecting into each rounded nostril; tip of snout darkened; jaws open, each covered by fleshy lips except anteriorly where horny portions exposed; dark triangular mark in front of eyes, base line uninterrupted, slightly curved anteriorly, connecting anterior margins of orbits; eyelids having blackish dots, especially upper, closing eyes; small blackish dots on dorsal surface of head; pale postocular stripe dark-bordered, interrupted; pale portion of stripe traversed by black line; pale subocular blotch margined by broken blackish border; side of head having contrasting blackish marks on pale background; postlabial stripe having lower blackish border on right side of head; chin with ill-defined marks, not contrasting on grayish background; well-defined, ragged black line on side of neck separating dorsal coloration from immaculate ventral coloration; small dark dots on dorsal surface of neck; dorsal surface of head and neck olive or brownish, becoming paler laterally and toward insertion of neck; maximum width of head, 2.1 centimeters.

Forefeet and hind feet well-webbed each having five digits; each limb having nails on first three digits; each forelimb with four antebrachial scales, three of which have free edge; each hind limb with two horny scales, one smooth on posterodorsal surface and other with free edge on posteroventral surface; contrasting pattern of blackish marks, mostly roundish, on pale background of grayish-white.

Tail terminating in flexible point; penis partly exposed; cloacal opening extending beyond posterior edge of carapace; tail having dorsal grayish band flanked by interrupted blackish lines; dark marks encroaching ventrally at tip of tail.

Undersurface of soft parts of body whitish, with pinkish tinge; dark marks lacking on soles, present on webbing and palms; dark marks arranged in linear fashion coincident with digits.

_Range._--Southern Oklahoma, eastern Texas, extreme southwestern Arkansas, and the western half of Louisiana; Red River drainage and rivers that drain into the Gulf of Mexico east of the Brazos River drainage in Texas and west of the Atchafalaya River drainage in Louisiana. The Brazos River drainage is inhabited by a population that more closely resembles _pallidus_ than _guadalupensis_ (see comments under subsection entitled "Remarks"; see map, Fig. 19).

_Diagnosis._--Juvenal pattern of white dots that are usually absent or inconspicuous, but sometimes distinct and small, on anterior third of carapace, and not surrounded with dark ocelli; white dots often absent on posterior half of carapace of hatchlings; white spots, rarely as large as two millimeters in diameter, not encircled with black ocelli on adult males; pale rim of carapace less than four times wider posteriorly than laterally.

_Description._--Plastral length of smallest hatchling, 3.3 centimeters (KU 50832); of largest male, 16.0 centimeters (SM 2375); of largest female, 30.5 centimeters (TU 13213).

Surface of carapace in hatchlings uniform pale brown or tan; small white tubercles absent or inconspicuous on anterior half of carapace, but evident on posterior half of carapace, sometimes well-defined (TU 481), but usually inconspicuous (TU 678, 490); pale rim of carapace less than four times wider posteriorly than laterally.

Adult males resembling description of holotype; small whitish tubercles or dots rarely two millimeters in diameter on posterior half of carapace, smaller and usually inconspicuous on anterior half of carapace (TU 13281, 486); well-defined whitish tubercles occasionally on anterior half of carapace (KU 40174); white tubercles not surrounded with black ocelli; pattern of white dots seemingly less contrasting in _pallidus_ than in _guadalupensis_, owing to pale brown or tan carapace; small tubercles along anterior edge of carapace equilateral or conical having sharp tips.

Large females usually having pale brown carapaces with slightly contrasting, brownish, mottled and blotched, patterns; white prominences often evident posteriorly and anteriorly in middle of carapace and in nuchal region; tubercles along anterior edge of carapace equilateral or conical in shape.

Pattern on side of head and snout variable and of no diagnostic value; postocular stripe uninterrupted having dark borders (UMMZ 92754), or interrupted having pale segment behind eye (TU 13282); other variations in pattern shown on TU 10170 and 15818; pale stripes on snout having dark inner borders that join and form acute angle (TU 381), or lacking dark inner borders and having uninterrupted dark line connecting anterior margins of orbits (TU 13280); other variations in pattern on snout shown on TU 1232, 1291 and 15819; specimens representing illustrations of variation in pattern on snout (Fig. 5 d, e, f) all from same locality, Lewisville, Lafayette County, Arkansas; contrasting pattern on side of head of dark marks on pale background; contrasting pattern of dark marks on dorsal surface of limbs; markings on hind limbs generally larger than those on forelimbs; small or fine markings of some specimens reducing contrast in pattern (TU 478, 488); carapace sometimes having few small blackish dots confined to margin (CNHM 15474, TU 487, 1253, 13266); ventral surface of plastron and soft parts of body whitish and usually lacking dark markings; small blackish marks often occurring on flap of carapace, in region of bridge, or on chin and throat (TU 399, 469, 475, 472, 13281).

Ontogenetic variation in PL/HW, mean PL/HW of specimens having plastral lengths 7.0 centimeters or less, 4.15, and exceeding 7.0 centimeters, 5.32; ontogenetic variation in CL/CW, mean CL/CW of specimens having plastral lengths 8.5 centimeters or less, 1.10, and exceeding 8.5 centimeters, 1.14; mean CL/PCW, 2.12; mean HW/SL, 1.38 (including subspecies _guadalupensis_); mean CL/PL, 1.36.

_Variation._--In 1953, I casually glanced at a hatchling softshell from the Calcasieu River drainage in the private collection of Mr. Wilfred T. Neill; the specimen was considered by Neill (1951:15) as "... an intergradient one (with the _hartwegi-spinifer_ population in the lower Mississippi drainage)." The hatchling does deviate from "typical" _pallidus_ in having darkish flecks posteriorly on the carapace.

I have seen only one adult male (USNM 94457) from the Sabine River drainage (Orange County, Texas) that shows characteristics of _guadalupensis_ (white dots on carapace encircled with small black ocelli); another adult male (USNM 94456) from the same locality resembles _pallidus_. Those two USNM specimens were mentioned by Neill (1951:13) as indicating intergradation with "... the mixed _spinifera-hartwegi-asper_ populations of Louisiana."

Two adult males (SM 2889, Pl. 40, bottom, left, and TCWC 471, Trinity River drainage) have blackish ocelli surrounding the white dots on the posterior part of the carapace; two large females (TU 14402, Pl. 40, bottom, right, plastral length, 17.5 cm., and TU 14417 plastral length, 21.3 cm., both from the Trinity River) have contrasting mottled and blotched patterns with white dots visible on the carapace. These turtles show alliance with _guadalupensis_.

Some individuals from the Brazos River drainage have features suggesting those that are characteristic of _guadalupensis_. Hatchlings may have large white dots on the anterior half of the carapace (USNM 55601). Adult males may have dusky ocelli surrounding the white dots on the carapace (TU 14169, 14559.1, 14559.2). The whitish dots, rarely as large as two millimeters, are never so large as in _guadalupensis_ (three mm. in diameter), and are usually smaller anteriorly than posteriorly; TU 14169 has white dots approximately the same size (1.2 mm.) on the anterior half as on the posterior half of the carapace. The tubercles on adult males are equilateral or subconical, usually having sharp tips (TU 14348, 14559.1, 14559.2); the tubercles on large females are subconical, resembling the end of a bullet, and, in both sexes the tubercles are less conical than those on specimens of _pallidus_ from farther east.

Three specimens from the Brazos River drainage are particularly impressive in their alliance with _guadalupensis_. SM 2556, an adult male, has large white dots that are encircled with black ocelli on the posterior half of the carapace, but lacks white dots on the anterior half. TNHC 14068, a hatchling, has small black dots interspersed with the larger white dots posteriorly. CNHM 46289 has large white spots on the carapace that are surrounded with two to four black dots; scattered black dots also intermix with white spots on the surface of the carapace (less extensive anteriorly).

Color notes taken from a freshly-killed adult male (KU 47121) from the Brazos River, seven miles below Whitney Dam, Bosque-Hill county line, Texas, are: Carapace pale brown or tan bordered by black line, having pale lemon yellow rim; yellowish-cream spots on carapace faintly surrounded with black stippling; dorsal surface of soft parts of body olive having black marks and patches of grayish; webbing on limbs having golden or yellowish hue, brighter distally; interorbital region brown; black-bordered, postocular stripe orange-cream; snout and side of head olive having pale areas of orange-cream; iris cream having black stripe; yellowish at juncture of dark dorsal and pale ventral coloration with orangish tinge on forelimbs and head; tail pale brown or tan, flanked by black borders that suffuse laterally into lemon-yellow; undersurface whitish, pale yellow on neck, bluish-gray on throat.

_Comparisons._--_T. s. pallidus_ most closely resembles _T. s. guadalupensis_, but can be distinguished from that subspecies in having small white tubercles, rarely two millimeters in diameter, on a pale background, that are not surrounded by blackish ocelli, and are usually absent, or not conspicuous on the anterior third of the carapace in adult males; also there are usually no conspicuous white tubercles or dots on the anterior third of the carapace in hatchlings. Many adult males of _pallidus_ from the Brazos and some from the Trinity River drainages often have dusky or black ocelli surrounding the white dots posteriorly on the carapace; males from these river systems may be distinguished from _guadalupensis_ in having most, if not all, white dots on the anterior half of the carapace smaller than those posteriorly, and a pale brown carapace (in life, usually darker in _guadalupensis_). _T. s. pallidus_ (and _guadalupensis_) is distinguished from _emoryi_ in lacking a widened pale rim posteriorly, and in having small white spots on the anterior half of the carapace. _T. s. pallidus_ resembles _guadalupensis_ and _emoryi_ in having white spots on the carapace in adult males. _T. s. pallidus_ differs from _spinifer_, _hartwegi_ and _asper_ in lacking blackish dots or ocelli that occur in the center of the carapace. _T. s. pallidus_ resembles _emoryi_ but differs from _guadalupensis_ in lacking black ocelli surrounding the white spots. _T. s. pallidus_ resembles _spinifer_, _hartwegi_ and _asper_ but differs from _guadalupensis_ and _emoryi_ in having tubercles along the anterior edge of the carapace that are conical having sharp tips in males, and conical in large females.

_T. s. pallidus_ resembles _spinifer_ and _hartwegi_ but differs from the other subspecies in having a narrow head. _T. s. pallidus_ differs from _emoryi_ but resembles the other subspecies in having a wider carapace. _T. s. pallidus_ resembles _emoryi_ and _guadalupensis_, and differs from the other subspecies in having the carapace widest farther posterior than one-half the length of the carapace. The snout of _pallidus_ and _guadalupensis_ is shorter than in _spinifer_ and _hartwegi_, but longer than in _emoryi_. _T. s. pallidus_ differs from _asper_ but resembles the other subspecies in having a relatively long plastron.

_Remarks._--Intergradation of the subspecies _pallidus_ and _guadalupensis_ is of a clinal nature in which populations successively show a gradual resemblance to _guadalupensis_ from western Louisiana and eastern Texas westward to central Texas. Because the sharpest break in this cline of characters occurs between the Colorado and Brazos River drainages, the turtles living in the Brazos River drainage and eastward are referred to _pallidus_, whereas those in the Colorado River drainage and westward are referred to _guadalupensis_. For further comments on intergradation between these two subspecies, see the account of _T. s. guadalupensis_.

Taylor (1935:217-18) reported on some specimens of _Amyda spinifera_ that were obtained by Mr. R. E. McEntyre in "... the spring and summer of 1926, chiefly about Lewisville, Lafayette County (Arkansas)." Of the catalog numbers listed by Taylor from Lewisville, 58 (KU, alcoholic) represent _pallidus_. Three, having the same locality data, have features that are characteristic of _hartwegi_. KU 2944 (one of three specimens having this catalog number) is a female having a pale, mottled and blotched carapace approximately one foot in length; there are remnants of two dark ocelli, and many widely-scattered, well-defined dark spots near the periphery of the carapace. KU 2963 (one of three specimens having this catalog number) is an adult male that has solid, blackish dots on the entire surface of the carapace. KU 2964 (one of two specimens with this catalog number) is an adult male that has ocelli approximately five millimeters in diameter on the carapace (indistinct in center of carapace).

Lewisville is situated in the drainage basin of the Red River and is approximately eight miles east of the Red River and 30 miles west of the westernmost tributary of the Ouachita River drainage. _T. s. pallidus_ occurs in the Red River drainage; _hartwegi_ occurs in the Ouachita River drainage. Perhaps there is intergradation between _pallidus_ and _hartwegi_ in the intervening streams. There is no data to indicate from which river or stream each specimen obtained by McEntyre came; one would presume that all specimens came from the Red River drainage. But this is not certain. Certainly the 47 specimens designated herein as _pallidus_ came from the Red River drainage. I suspect that KU 2944, 2963 and 2964 were obtained from tributaries of the Ouachita River drainage.

_T. s. pallidus_ intergrades with the _spinifer-hartwegi_ population where the Red River joins the Mississippi River in the lower Mississippi Valley in Louisiana. The majority of 13 juvenal specimens from the Red River near Shaw, Concordia Parish, Louisiana (USNM 99862-69, 99871-75), resemble _pallidus_ in having inconspicuous white tubercles on a pale brown carapace. The white tubercles are conspicuous in USNM 99871. Some specimens have a few small dark dots confined to the margin of the carapace, as do some "variant" individuals from well within the geographic range of _pallidus_. USNM 99865 is referred to _hartwegi_ because the carapace is covered with dark ocelli approximately one millimeter in diameter. Some specimens from farther west in the Red River drainage are referred to _hartwegi_. One (USNM 100420) of three from Natchitoches Parish, Louisiana (TU 5763, USNM 100420-21), having blackish dots on the carapace, is applicable to _hartwegi_. Of two turtles from Grant Parish, Louisiana (TU 5647, 12735), only 12735 has dark dots and ocelli (_hartwegi_). One specimen from Rapides Parish, Louisiana (TU 14040), having dark dots on the entire surface of the carapace, is referred to _hartwegi_.

Most specimens from the lower Atchafalaya River drainage are referable to _pallidus_. Eastward, intergradation occurs with the _spinifer-hartwegi_ population; USNM 100089-90 from Assumption Parish, near Napoleonville, Louisiana, are referred to _pallidus_. TU 11983, from Bayou Lafourche, Raceland, La Fourche Parish, and TU 13698.11, from Bayou Gauche in St. Charles Parish, Louisiana, are juvenal males that combine the characteristics of _pallidus_ and _hartwegi_; the carapaces are covered with blackish spots and posteriorly have distinct whitish dots. The population in the Atchafalaya River more closely resembles _pallidus_ than it does _hartwegi_ or _spinifer_. In former times the Atchafalaya River was presumably continuous solely with the Red River (inhabited by _pallidus_). Now, these two rivers and the Mississippi River are interconnected in east-central Louisiana. A large volume of water of the Mississippi drainage is conveyed to the Gulf of Mexico by the Atchafalaya, and someone has said that by approximately 1975, unless man interferes, two-thirds to three-fourths of the total volume of water of the Mississippi River will be drained by the Atchafalaya. One can expect, therefore, an increase in the influence of the _hartwegi-spinifer_ population in the Atchafalaya River drainage.

_Specimens examined._--Total 270, as follows: ARKANSAS: _Lafayette_: KU 2930-37, 2939-40, 2942, 2944 (two of three specimens bear this catalog number), 2945-57, 2958 (2), 2959-61, 2963 (two of three specimens bear this catalog number), 2964 (one of two specimens bears this catalog number), 2965-73, 2987-89, 3056, Lewisville.

LOUISIANA: _Acadia_: USNM 100151-59, Mermentau River. _Assumption_: USNM 100089-90, Bayou Lafourche, "near" Napoleonville. _Beauregard_: TU 1231-32, 1253-55, 1291, 13211, 13266, Sabine River, 8 mi. SW Merryville. _Bienville_: TU 5649-50, Lake Bistineau. _Caddo_: TU 381, 397-99, 469-72, 474-90, 678, 10170, Caddo Lake: TU 15818-19, Cross Lake. _Calcasieu_: UMMZ 92754, 5 mi. W Iowa. _Cameron_: TU 1122, Lacassine Wildlife Refuge. _Concordia_: USNM 99862-64, 99866-69, 99871-75, Red River, "near" Shaw. _De Soto_: SM 2374-75, Wallace Bayou. _Grant_: TU 5647, Lake Iatt. _Iberville_: USNM 83985, 2 mi. E Mounds; USNM 100239-41, Grand Lake west of White Castle; USNM 100380, Plaquemine; USNM 100412, 100414-15, 100419, Spanish Lake, "near" St. Gabriel. _Jefferson Davis_: Calcasieu River drainage, WTN (no number, see page 524). _Natchitoches_: TU 5763, Bermuda; USNM 100421, "near" Natchitoches. _Sabine_: TU 13210, 13212-13, 13265, 13280-82, 13303-06, Sabine River, 8 mi. SW Negreet. _St. Martin_: USNM 100160, Bayou Chene; USNM 100650, Atchafalaya. _St. Mary_: USNM 100395-97, 100404, 100409-10, Berwick Bay near Morgan City.

OKLAHOMA: _Atoka_: OU 8966, Rock Creek, 10 mi. E Atoka; OU 8978, McGee Creek, 7 mi. SW Daisy. _Caddo_: ANSP 100, Washita River, Fort Cobb. _Choctaw_: OU 27126, Mayhew Creek, 2 mi. NW Boswell. _Comanche_: OU 4130, 4266, 5390, 8333, 12953, 19986, Wichita Mountains Wildlife Refuge. _Jackson_: OU 13012, 6 mi. E El Dorado. _Kiowa_: CNHM 15474. _Le Flore_: OU 6791, Kiamichi River, 8 mi. W Arkansas State Line. _McCurtain_: OU 2149-50, 2152, 2155, 17126-28, 17185, 2 mi. SW Smithville; USNM 70397, Red River. _Marshall_: KU 40175-76, 50830-31, 50847, OU 27290, 27297, 27562-63, TU 16076 (5), 16175 (6), 16662 (5), Lake Texoma, 2 mi. E Willis; KU 50832, mouth of Caney Creek, 4 mi. SW Kingston. _Pushmataha_: OU 2151, 2157; OU 11365, Buffalo Creek, 5 mi. NW Tuskahoma.

TEXAS: _Archer_: TU 16174, 16668-69, Lake Diversion. _Bell_: SM 5667-69, Nolan Creek. _Bosque_: KU 47121, 7 mi. below Whitney Dam, Brazos River. _Brazos_: BCB 4436, 10 mi. E College Station; BCB 4437, 17 mi. S College Station; BCB 4438, 4 mi. N Bryan; KU 50833, 4 mi. W College Station; SM 2556, TCWC 472, Wickson Lake; TCWC 539, Little Brazos River; TCWC 4692, 8 mi. NE Bryan; TCWC 5121, 2 mi. S College Station; TCWC no number. _Clay_: TCWC 7258, 8 mi. NW Ringgold, Montague County; TU 16667.1, 3 mi. W Byers. _Dallas_: MCZ 3987, "near" Dallas; ANSP 13243, Dallas. _Donley_: ANSP 13440, S of Clarendon. _Eastland_: KU 3132, Cisco. _Galveston_: TCWC 7251, Alta Loma. _Harris_: UMMZ 92753, Little Cypress Creek, 1 mi. N Westfield; USNM 94335-36, "near" Houston. _Harrison_: USNM 95386, 16.5 mi. SE Caddo Lake. _Hill_: TU 14169, Richland Creek, 0.7 mi. W Mertens. _Leon_: CNHM 46290, 5 mi. W Marquez; TCWC 8994, 8996, 6 mi. NW Normangee. _Liberty_: TU 14402, 14417, Trinity River, "near" jct. with Big Creek. _McLennan_: BCB 4665-66, 6 mi. NNE McGregor; SM no number, 2037, 2452, 2552, 2558, 2560, 2640, 5263, 6533, Lake Waco; SM 0185, Middle Bosque River; SM 2104, 6732, Upper Bosque River; SM 5072, Bull Hide Creek; UI 2399, 1.5 mi. W China Springs; UMMZ 64063, Waco; USNM 55601. _Madison_: TCWC 471, 517, Twin Lakes. _Montgomery_: TCWC 540, 3 mi. S Conroe. _Nacogdoches_: TNHC 14112, Legg Creek, 5 mi. S Douglass. _Orange_: UMMZ 117060, 3 mi. S Orange; USNM 94456-57, Orange. _Randall_: TTC 576, Palo Duro Canyon, 15 mi. SE Canyon. _Shackelford_: TU 14547, Clear Fork Brazos River, Fort Griffin State Park. _Somervell_: TCWC 8995, TU 14559 (4), Brazos River, 5-6 mi. E Glen Rose. _Trinity_: SM 2889, Groveton. _Walker_: TNHC 20829, 5 mi. E New Waverly. _Waller_: TNHC 14068, 2.7 mi. E Brazos River on US 90. _Williamson_: MCZ 1627 (2); TU 14348, San Gabriel River, 6.5 mi. E Georgetown. _County unknown_: ANSP 13448, Wichita River; USNM 7640, Brazos River.

_Records in the literature._--LOUISIANA: _Cameron_: Sabine Refuge (Cagle and Chaney, 1950:386).

OKLAHOMA: _Le Flore_: 6 mi. W Page. _McCurtain_: 14 mi. SE Broken Bow (Trowbridge, 1937:301).

TEXAS: _Bosque_: Bosque River, "near" Valley Mills (Strecker, 1928:6). _Harris_: Addicks (Brown, 1950:250). _Henderson_: Cedar Creek (Strecker, 1926a:7). _Jefferson_: 12 mi. SW Port Arthur (Guidry, 1953:56). _Liberty_: Daisetta (Brown, _loc. cit._); San Jacinto River (Strecker, 1915:15). _McLennan_: "near" Crawford (Brown, _loc. cit._). _Orange_: 1 mi. N Bridge City (Guidry, _loc. cit._). _Tarrant_: Trinity River, Fort Worth (Stejneger, 1944:66). _Taylor_: Abilene (KKA). _Tyler_: Colmisneil (Siebenrock, 1909:603). _Walker_: 6 mi. E Huntsville (TCWC 329, listed in card file). _Wheeler_: 5 mi. N Wheeler (Brown, _loc cit._).

=Trionyx ater= Webb and Legler

Black Softshell

_Trionyx ater_ Webb and Legler, Univ. Kansas Sci. Bull., 40:21,
pls. 1 and 2, 1960, April 20.

_Type._--Holotype, KU 46903, alcoholic female; obtained 16 km. S Cuatro Ciénegas, Coahuila, México, by John M. Legler (and party), September 6, 1958.

_Range._--Basin of Cuatro Ciénegas, central Coahuila, Mexico (see map, Fig. 22).

_Diagnosis._--Posterior margin of carapace of some females having fine corrugations, edge often ragged, and no pale outer margin; septal ridges reduced in adult males; over-all dorsal coloration (in preservative) dark, lacking contrasting patterns.

_Description._--Plastral length of adult male, 9.6 centimeters (KU 46911); of largest female, 18.4 centimeters (KU 46903).

Adult male: anterior edge of carapace smooth; septal ridges reduced; pale outer rim, and small, whitish, dots posteriorly on carapace; surface of carapace slightly gritty or sandpapery posteriorly; snout broadened; over-all dorsal coloration dark gray or slate; contrasting pattern on soft parts of body lacking; ventral surface whitish having few blackish marks posteriorly on undersurface of carapace.

Females: posterior margin of carapace usually having fine corrugations; edge of carapace posteriorly often ragged; pale rim of carapace absent; mottled and blotched pattern not contrasting on blackish carapace; dorsal surface of soft parts of body dark gray or slate, lacking contrasting pattern; ventral surface of carapace and posterior part of plastron usually having many blackish flecks and markings; tubercles lacking on anterior edge and in center of carapace posteriorly; septal ridges well developed.

Medial angle of epiplastron (as observed through overlying skin) bent at angle of approximately 90 degrees. Other osteological characters presumably as in _spinifer_.

Range in length of plastron (cm.) of 11 females (mean follows extremes); 10.8-18.4, 15.0; proportional measurements of 12 specimens (including adult male, mean follows extremes): PL/HW, 4.70-5.43, 4.93; CL/CW, 1.28-1.43, 1.32; CL/PCW, 1.98-2.42, 2.15; HW/SL, 1.22-1.58, 1.37; CL/PL, 1.29-1.44, 1.36; some females (especially KU 46908) have noticeably elongate carapaces.

_Variation._--Corrugations best developed on two largest females (KU 46903, 46906), even present on ventral surface of carapace posteriorly and on dorsal surface of tail; development of corrugations not ontogenetic phenomenon as posterior margin relatively smooth on KU 46908 (plastral length, 16.0 cm.) but relatively rugose on KU 46909, which is smaller (plastral length, 13.9 cm.); smallest female (KU 46904) and adult male having posterior margin smooth; smallest female having indication of pale outer rim and small whitish dots posteriorly on carapace, and dark, obtusely-angular line, connecting anterior margins of orbits; blackish marks on ventral surface reduced on KU 46904, 46910, 46912, and UI 43510; UI 43510 (plastral length, 16.3 cm.) resembles _T. s. emoryi_ in having more contrasting mottled pattern on carapace and limbs, indication of pale outer rim on carapace, and dark line connecting anterior margins of orbits; ventral surface of tail and hind limbs often tinged with red.

Color notes from life of young female, topotype (KU 53755) are: mottled carapace dark brown, pale areas buff; dorsal surface of head mottled, olive-brown, pale areas buff; iris orange-buff; upper and lower lips yellow-orange; dorsal surface of limbs olive-brown having yellow to buff suffusion and small blackish marks; pale areas on webbing yellow; ventral surface whitish having yellow at margin of carapace, on neck and limbs.

_Comparisons._--_T. ater_ most closely resembles _T. spinifer_ (especially the subspecies _emoryi_) in having a gritty or "sandpapery" carapace (reduced, tubercles more scattered), whitish dots on posterior third of carapace (small females and adult male) and a dark line connecting anterior margins of orbits (smallest female). Prior to acquiring the characteristic darkened, dorsal ground color, the pattern on the head and limbs seems to be that of _T. s. emoryi_.

_T. ater_ resembles _T. muticus_ in having reduced septal ridges in males, a smooth anterior edge of carapace (especially males), and no enlarged prominences on the anterior edge of the carapace or posteriorly in the center of the carapace on large females. _T. ater_ resembles _T. ferox_ in having an over-all dark coloration dorsally with no contrasting patterns on adults.

_T. ater_ probably is a small species resembling _T. muticus_ and _T. spinifer emoryi_. The head is wide in _T. ater_, resembling that of _T. ferox_, and closely approaching that of _T. spinifer emoryi_ and _T. s. guadalupensis_. _T. ater_ resembles _T. ferox_ and _T. s. emoryi_ in having a narrow carapace. _T. ater_ resembles _T. s. emoryi_, _T. s. guadalupensis_ and _T. s. pallidus_, but differs from _T. muticus_, _T. ferox_ and the other subspecies of _T. spinifer_ in having the carapace widest farther posterior than one-half the length of the carapace. _T. ater_ resembles _T. ferox_ and _T. s. emoryi_ in shortness of snout. The plastron is short in _T. ater_ and most closely resembles that of _T. s. pallidus_, _T. s. guadalupensis_, and _T. s. emoryi_.

_Remarks._--_T. ater_ is confined to permanent, clear-water ponds in the basin of Cuatro Ciénegas. The male and 11 females (KU) were taken at the type locality (a pond known locally as Tío Candido); the other female (UI 43510) was taken from a pond approximately seven miles northward (known locally as Anteojo). _T. spinifer emoryi_ also occurs in the basin of Cuatro Ciénegas. Males and females of _emoryi_ were collected in the Río Mesquites (Río Salado drainage) that drains the basin; two adult males of _emoryi_ were taken from the clear-water ponds--one from the type locality of _ater_ (KU 46907), and the other (KU 53757) from a pond (known locally as El Mojarral) from which no _ater_ were obtained. This demonstrated sympatry indicates that the two kinds are not conspecific.

However, the nature and frequency of occurrence of characters of _T. ater_, suggest that it is subspecifically related to _T. spinifer_--in effect, a darkened race of _T. s. emoryi_. The diagnostic characters of fine corrugations on the posterior margin of the carapace and blackish marks on the ventral surface do not occur on every female of _ater_. Too, the dorsal coloration of living females (dark brown-buff) is paler than that of preserved specimens (dark gray-slate). Furthermore, a hatchling (CNHM 47367) recorded from Cuatro Ciénegas, Anteojo, is not distinguishable from _emoryi_.

The mention of absence of septal ridges in males of _T. ater_ in the original description (Webb and Legler, 1960:22) should be amended. The septal ridges in the only known adult male are reduced; a small, whitish ridge is present on the medial surface of each nostril, but is not conspicuous in anterior view. The one adult male of _ater_ is distinguished from _T. s. emoryi_ principally on the over-all dark, dorsal coloration with concomitant loss of pattern, the noticeably broadened snout, and the reduced septal ridges. The last character mentioned possibly is variable in _ater_ (and in _emoryi_ in this region) in view of the variation in development of the ridge on four male _emoryi_ from the basin: well-developed on KU 53757 (Mojarral) and KU 46907 (Tío Candido); reduced on KU 53752 (Río Mesquites), resembling development in _ater_; and, reduced on right side only on KU 53753 (Río Mesquites).

Presumably, the continued erosive action at the headwaters of the Río Salado has permitted the invasion of this drainage into the formerly isolated basin of Cuatro Ciénegas. In the basin, however, I know of no evidence of a direct aquatic contact between the headwater streams and the isolated, clear-water, ponds. How _emoryi_ entered the ponds is unknown. Some of the ponds are tapped by small, man-made, irrigation canals, but, so far as I know, these are not connected to the river. The ponds have permanent water and are often separated by several miles of arid environment. Overland dispersal between waterways is possible in time of flooding. Local residents tell of the infrequent sale of softshells in Cuatro Ciénegas, which hints at their dispersal via the agency of man. The underlying gypsum substrate of the valley has been subjected to considerable erosion; the ponds observed have deep holes, and small caverns and grottos. There are conflicting reports concerning subterranean connections between ponds. Possibly there are underwater connections between some ponds and the headwater streams of the Río Mesquites. Whatever the dispersal route for _emoryi_ into the ponds has been, it is strange that the same route has not been traversed by _ater_, permitting its occurrence in the Río Mesquites.

On the basis of morphological criteria, I suspect that _ater_ and _emoryi_ are genetically compatible. Possibly there is only sporadic entrance of _emoryi_ into the ponds inhabited by _ater_, or the accessible dispersal routes for _emoryi_ have been relatively recent and there has been insufficient time for genetic adaptation. _T. ater_ is maintained as a full species because of the occurrence of two distinct males (KU 46907, _emoryi_, and KU 46911, _ater_) in the same pond (Tío Candido, the type locality). These two specimens are contrasted in a photograph accompanying the type description (Webb and Legler, 1960: Pl. II). The restricted distribution of _ater_, and its characteristics suggest a relict population derived from a _ferox_-like ancestor that may be in the process of becoming extinct.

There are two specimens in the CNHM recorded from Cuatro Ciénegas. One is a female (CNHM 55661) having a plastral length of 19.0 centimeters, and no specific locality other than Cuatro Ciénegas. I examined this specimen before I knew of the existence of _ater_, and noted no unusual features; I have not re-examined the specimen. It is considered representative of _emoryi_. The second is a hatchling (CNHM 47367) having a plastral length of 3.2 centimeters, recorded from Cuatro Ciénegas, Anteojo. The carapace is dark tan having small whitish dots intermixed with a few indistinct, small, blackish specks posteriorly. The specimen is indistinguishable from _emoryi_.

_Specimens examined._--Total 12, as follows: COAHUILA: KU 46903-06, 46908-12, 53755-56, 16 km. S Cuatro Ciénegas; UI 73510, 5.7 mi. W Cuatro Ciénegas.

_Records in the literature._--Schmidt and Owens (1944:103) record _emoryi_ from Cuatro Ciénegas (no museum numbers listed); presumably their reference is to CNHM 55661.

=Trionyx muticus= Lesueur

Smooth Softshell

_Range._--United States from extreme western Pennsylvania, southern Minnesota and South Dakota south to the Gulf of Mexico in Alabama, the western end of the panhandle of Florida, and the eastern half of Texas (see map, Fig. 22.)

_Diagnosis._--Septal ridges absent; anterior edge of carapace smooth, lacking prominences; juvenal pattern of large dusky spots (sometimes ocellate), or small dusky (not black), dots and short lines; side of head usually devoid of markings except for pale, usually uninterrupted, postocular stripe.

Size small; head narrow; snout long; ventral surface of supraoccipital spine broad proximally, lacking median ridge; foramen magnum evenly rounded, ovoid; opisthotic-exoccipital spur absent; distal part of opisthotic wing truncate; lateral condyle of articular surface of quadrate tapered posteriorly, smaller than medial articular surface; angle of epiplastron obtuse, approximately 100 degrees; callosity on epiplastron sometimes covering entire surface; bony bridge wide in relation to length.

_Description._--Septal ridges absent; external characteristics variable (see accounts of subspecies); range in length, in centimeters, of plastron of ten largest specimens of each sex, (mean follows extremes), males, 11.8-14.0, 12.3; females, 17.7-21.5, 18.9; ontogenetic variation in PL/HW, mean PL/HW of specimens having plastral lengths 7.0 centimeters or less, 4.16, ranging from 7.1 to 13.0 centimeters, 5.82, and, exceeding 13.0 centimeters, 7.04; little ontogenetic variation in CL/CW, mean CL/CW of specimens having plastral lengths 8.0 centimeters or less, 1.15, and exceeding 8.0 centimeters, 1.16; mean CL/PCW, 1.97; mean HW/SL, 1.22; mean CL/PL, 1.39.

Greatest width of skull usually at level of squamosal (79%); foramen magnum ovoid; opisthotic-exoccipital spur usually absent (97%); distal part of opisthotic wing truncate, sometimes visible in dorsal view; lateral condyle of articular surface of quadrate tapered posteriorly, smaller than medial articular surface; maxillaries not in contact above premaxillaries; combination of seven neurals, seven pairs of pleurals, and contact of seventh pair of pleurals (38%), or eight neurals, seven pairs of pleurals, and separation of seventh pair of pleurals (41%); angle of epiplastron obtuse, greater than 90 degrees; callosities well-developed, frequently on preplastra and epiplastron of adults.

_Comparisons._--The absence of septal ridges distinguishes _muticus_ from _ferox_, all subspecies of _spinifer_, and _ater_ (ridges are reduced in males of _ater_). The smooth anterior edge of the carapace distinguishes _muticus_ from all other American kinds except _ater_ and some individuals of _T. s. emoryi_. _T. muticus_ resembles only _ater_ and _ferox_ in usually lacking a well-defined, contrasting pattern of blackish marks on the dorsal surface of the limbs. _T. muticus_ resembles _ferox_ and differs from _spinifer_ and _ater_ in lacking a gritty or "sandpapery" carapace on adult males. Adult males of _T. muticus calvatus_ and some individuals of _T. m. muticus_ from the Colorado River in Texas further resemble _ferox_ in having postocular stripes with thick black borders.

_T. muticus_ is the smallest species in North America; the maximum size of the plastron in adult males is approximately 14.0 centimeters (16.0 cm. in _spinifer_) and of adult females 21.5 centimeters (31.0 cm. in _spinifer_). Males and females of _muticus_ are sexually mature at approximately the same size as some _T. s. emoryi_; also, the great development of the plastral callosities in _muticus_ corresponds to that in some _emoryi_. The head is narrower in _muticus_ than in _ferox_ or _spinifer_. The carapaces of specimens of _muticus_ exceeding plastral lengths of 8.0 centimeters are wider than those of _ferox_, _ater_, _T. s. emoryi_ and _T. s. guadalupensis_ of corresponding size. _T. muticus_ differs from _ater_ and three subspecies of _spinifer_ (_pallidus_, _guadalupensis_, _emoryi_) in having the carapace widest at a plane approximately one-half the length of the carapace. The snout is longer in _muticus_ than in _ferox_ and _spinifer_. _T. muticus_ differs from _ferox_ but resembles _spinifer_ in having a relatively short plastron.

The skulls of _muticus_ differ from those of _ferox_ but resemble those of _spinifer_ in usually having the skull widest at the level of the squamosals. Skulls of _muticus_ resemble those of _ferox_ but differ from those of _spinifer_ in usually lacking a well-developed opisthotic-exoccipital spur. Skulls of _muticus_ are different from those of _ferox_ and _spinifer_ in having the 1) ventral surface of the supraoccipital spine widest proximally, lacking a medial ridge, 2) foramen magnum ovoid, 3) distal part of opisthotic wing truncate, 4) lateral condyle of articular surface of quadrate tapered posteriorly, smaller than medial articular surface, and 5) maxillaries not in contact above premaxillaries.

Plastrons of _muticus_ differ from those of _spinifer_ and _ferox_ in having an obtusely-angled epiplastron, relatively large callosities in adults, and a wide hyo-hypoplastral bridge (in relation to length).

_Remarks._--Agassiz (1857:399) regarded Lesueur's _Trionyx muticus_ as the type species of the genus _Amyda_ and the only species known to belong to the genus _Amyda_. Stejneger (1944:7, 9, 12) proposed the generic name _Euamyda_ as a new name for the North American _Amyda mutica_ as understood by Agassiz. _Euamyda_ was proposed for use only if Agassiz's understanding was found to be correct. Actually, Stejneger thought that the Old World and New World kinds concerned were congeneric, and that the type species of the genus _Amyda_ was the Old World species _Amyda javanica_ Schweigger (= _Testudo cartilaginea_ Boddaert).

If _Trionyx muticus_ Lesueur is considered to be generically distinct from other soft-shelled turtles, _Euamyda_ Stejneger, 1944, is available as a generic name with _Trionyx muticus_ Lesueur, 1827, as the type species (by monotypy).

_Geographical variation._--_Trionyx muticus_ shows no obvious character gradients; the variation is mostly discontinuous and unlike that in _T. spinifer_. On the basis of differences in the juvenal pattern and pattern on head, _T. muticus_ can be divided into two subspecies.

=Trionyx muticus muticus= Lesueur

Midland Smooth Softshell

Plates 45, 46, and 53