North American Recent Soft-shelled Turtles (Family Trionychidae) Part 16

_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 Cienegas. The male and 11 females (KU) were taken at the type locality (a pond known locally as Tio 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 Cienegas. Males and females of _emoryi_ were collected in the Rio Mesquites (Rio 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 Cienegas, 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_ princ.i.p.ally 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 (Tio Candido); reduced on KU 53752 (Rio Mesquites), resembling development in _ater_; and, reduced on right side only on KU 53753 (Rio Mesquites).

Presumably, the continued erosive action at the headwaters of the Rio Salado has permitted the invasion of this drainage into the formerly isolated basin of Cuatro Cienegas. 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 ca.n.a.ls, 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 softsh.e.l.ls in Cuatro Cienegas, 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 Rio 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 Rio 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 (Tio 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 Cienegas. One is a female (CNHM 55661) having a plastral length of 19.0 centimeters, and no specific locality other than Cuatro Cienegas. 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 Cienegas, 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 Cienegas; UI 73510, 5.7 mi. W Cuatro Cienegas.

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

=Trionyx muticus= Lesueur

Smooth Softsh.e.l.l

_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.)

[Ill.u.s.tration: FIG. 22. Geographic distribution of _Trionyx ater_ and _Trionyx muticus_. 1. _T. muticus muticus_. 2. _T. muticus calvatus_. 3. _T. ater_.]

_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 s.e.x, (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 s.e.xually 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._--Aga.s.siz (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 Aga.s.siz. _Euamyda_ was proposed for use only if Aga.s.siz'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-sh.e.l.led 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 Softsh.e.l.l

Plates 45, 46, and 53

_Trionyx muticus_ Lesueur, Mem. Mus. Hist. Nat. Paris, 15:263, pl.7, December, 1827.

_Trionyx muticus muticus_ Webb, Publ. Mus. Nat. Hist. Univ. Kansas, 11:520, August 14, 1959.

_Potamochelys? microcephala_ Gray, Proc. Zool. Soc. London, p. 87, 1864.

_Type._--Lectotype, Museum d'Histoire Naturelle, Paris, No. 8813; dried carapace and plastron; obtained from the Wabash River, New Harmony, Posey County, Indiana, by C. A. Lesueur in August, 1827 (Pl.

53).

_Range._--Central United States; in the Mississippi River drainage from extreme western Pennsylvania, southern Minnesota and South Dakota south to Tennessee, Louisiana and Oklahoma; streams of the Gulf Coast drainage from the Mississippi River in Louisiana westward into Texas including the Colorado River drainage (see map, Fig. 22).

_Diagnosis._--Juvenal pattern of dusky dots and usually short lines or bacilliform marks; ill-defined pale stripes on snout usually evident just in front of eyes; pale postocular stripe lacking thick, black borders that are approximately one-half width of pale stripe (except some in the Colorado River drainage of Texas).

_Description._--Plastral length of smallest hatchling, 2.1 centimeters (INHS 3458); of largest male, 14.0 centimeters (CNHM 92003); of largest female, 21.5 centimeters (KU 2308).

Juvenal pattern of dusky, grayish marks lacking sharp margins, and usually consisting of both small spots and short streaks or dashes, the former predominating; short streaks or dashes occasionally lacking (TU 14375, Pl. 45, bottom, left; UMMZ 92751); markings variable in number, few and widely s.p.a.ced, or several and closely approximated (Pl. 45, top, topotypes); pale rim separated from ground color by ill-defined, dusky margin; pattern on adult males well-defined resembling that of hatchlings (TU 16172.1, 16173), scarcely discernable (TU 13294), or absent (TU 1242); mottled and blotched pattern on carapace usually contrasting in large females.

Pale stripes extending forward from eyes usually not more than half distance to tip of snout; inner borders of pale stripes on snout usually absent or dusky and indistinct, occasionally blackish (TU 14606); outer borders of pale stripes darker than inner borders, usually blackish; pale stripes on snout occasionally absent (CNHM 7845, UMMZ 92665, TU 5989, none of these specimens being large females); pale postocular stripe having narrow, dusky or blackish borders (especially UMMZ 92751, TU 14436); pale postocular stripe usually complete, occasionally interrupted having prominent dark-bordered anterior segment just behind eye (TU 14416); lower border of postocular stripe usually in contact with dusky postl.a.b.i.al line; no other markings on side of head; pattern on dorsal surface of soft parts of body not contrasting, composed of closely approximated fine markings that are little darker than background, over-all coloration pale grayish; occasionally, few larger and more contrasting markings on hind limbs (UMMZ 92751, TU 14436).

Underparts white, usually lacking markings; occasional dusky markings on plastral area (UMMZ 110502), dark spots or flecks on undersurface of carapace (BCB 6043, UMMZ 92666), or markings on throat (UMMZ 95032).

Surface of carapace smooth in adult males; large females lacking prominences posteriorly in center of carapace or in nuchal region; anterior edge of carapace smooth in both s.e.xes, but occasionally having regularly s.p.a.ced furrows or wrinkles (Fig. 8g).

_Variation._--Short dusky lines and streaks seem to be lacking from the juvenal pattern on the carapace more often in southern populations (Gulf Coast drainage of Texas) than in northern populations (Mississippi River drainage). I have seen one female, KU 48229 (Pl.

46, bottom, left), plastral length 14.5 centimeters that retained a well-defined juvenal pattern, and lacked a mottled and blotched pattern.

Color notes from life of 11 turtles, KU 55296-306, (eight adult males, three immature females) from the Kansas River at Lawrence, Douglas County, Kansas, are: Buff-yellow rim of carapace, sometimes having pale orange tinge; dusky, dark brown markings on pale brown or tannish carapace of males; dark and pale brown mottled and blotched pattern on carapace of females (smallest specimens having plastral length, 11.0 cm.), many having orangish or buffy hue; soft parts of body brownish to olive-green dorsally, many having small, blackish marks on hind limbs; webbing of limbs yellowish; pale orange, some yellow, laterally at juncture of dark dorsum and pale ventrum (to a lesser extent on hind limbs); pale orange in some suffusing onto dorsal surface of soft parts of body; black-bordered postocular stripes in males having orangish tinge (pattern somewhat obscured in females); whitish ventral surface in some having pale orangish tinge here and there; many having dusky, grayish flecking on plastral area and anterior ventral surface (most intense on 55306 giving appearance of grayish suffusion).