spinifer_ (b); sculpturing of callosities incompletely shown. ep,
epiplastron; hp, hyoplastron; hyp, hypoplastron; pp, preplastron;
xp, xiphiplastron. a--KU 1868, White River, Devall's Bluff, Prairie
County, Arkansas (× 2/3); b--KU 1869, same locality (× 2/3).]
Much importance has been credited to the fusion (no suture) or
separation (suture present) of the hypoplastra and hyoplastra. The
fusion of these bones distinguishes the genera _Lissemys_, _Cyclanorbis_
and _Cycloderma_ from _Trionyx_, _Pelochelys_, and _Chitra_ (Siebenrock,
_op. cit._:815, 817; Loveridge and Williams, 1957:415). This character
is also one of the criteria used by Hummel (1929: 768) in his erection
of the two subfamilies Cyclanorbinae (= Lissemyinae) and Trionychinae.
In my examination of specimens this character, unfortunately, was not
given full attention. I have noted the fusion of the hypoplastra and
hyoplastra in KU 1878 (_muticus_, right side only), KU 2219 (kyphotic
_spinifer_), KU 16528 (_ferox_) and KU 60121 (_ferox_). Dr. Ernest E.
Williams informs me in a letter of November 17, 1959, that of six
specimens of _ferox_ in the MCZ, the hyoplastra are fused with the
hypoplastra in three (54689-90, 54686). I suspect that these bones in
the three American species of the genus _Trionyx_, especially in
_ferox_, fuse more often than is supposed.
In _muticus_ the constricted part of the hyoplastron and hypoplastron is
wider anteroposteriorly than in _spinifer_ or _ferox_ (Fig. 17).
The three American species have on the hyoplastra, hypoplastra, and
xiphiplastra well-developed callosities, which enlarge with increasing
size. The medial borders of the hyoplastral and hypoplastral callosities
in larger specimens are rounded and closely approximated, often
touching, as do the callosities of each xiphiplastron; seemingly, the
callosities are relatively larger in _muticus_ than in _spinifer_ and
_ferox_. I have seen one adult male _muticus_ (KU 41380) that lacked
median fontanelles or vacuities owing to the contact of the plastral
elements (as viewed through overlying skin, alcoholic specimen). The
bony plastron (approximately 9 cm. in maximal length) of a small
_muticus_ (KU 19460) resembles the plastron of larger individuals of
_muticus_ in having well-developed hyoplastral and hypoplastral
callosities that are closely approximated medially. Large individuals of
_muticus_ usually have small, ovoid callosities on the preplastra, and a
well-developed, angular callosity on the epiplastron (Fig. 17a).
Siebenrock (_op. cit._:823) suggests that the presence of callosities on
the preplastra and epiplastron of _muticus_ is subject to individual
variation. I can not substantiate or dispute the supposition of Baur
(1888:1122), Siebenrock (1924:193) and Stejneger (1944:12, 19) that the
callosities are larger in males of _muticus_ than in the females. Some
individuals of _spinifer_ have seven plastral callosities (KU 2842) as
does _muticus_, but the callosities on the preplastra and epiplastron
are less frequent and less well-developed in large specimens of
_spinifer_ than in _muticus_. The small epiplastral callosity in
_spinifer_ is located at the medial angle and does not extend
posterolaterally to cover the entire surface of the epiplastron as it
may in _muticus_ (Fig. 17b). The epiplastron of a _spinifer_ (KU 2826)
has a medial callosity and another on the right posterolateral
projection; three separate callosities occur on the epiplastron of MCZ
46615. The last specimen mentioned, a large, stuffed female, possesses a
round, intercalary bone that tends to occlude the posteromedial vacuity.
Seemingly, the callosity on the epiplastron appears prior to those on
the preplastra; I have not seen any plastra having callosities on the
preplastra and lacking a callosity on the epiplastron. I have not noted
callosities on the preplastra or epiplastron of specimens of _ferox_.
The callosities on the plastral bones are sculptured; small, recently
formed callosities on the preplastra and epiplastron lack sculpturing.
The pattern of sculpturing on the plastral bones as well as that of the
carapace is generally of anastamosing ridges. I am unable to discern any
differences in pattern of sculpturing between the three American
species. Stejneger distinguished adult specimens of _ferox_ from the
other American species by the coarseness of the sculpture of the bony
callosities (1944:24) and of the bony carapace (_op. cit._:32). The
sculpturing on the plastral callosities and carapace seems to be
correlated with size; larger specimens (_ferox_) have coarser
sculpturing than do smaller specimens (_muticus_). Stejneger also
mentioned that the sculpturing on many specimens of _ferox_ is
specialized into prominent, longitudinal welts (_loc. cit._); these
welts occur also on the carapace of _spinifer_.
On the basis of the osteological characters examined by me, _T. muticus_
is distinguished from _spinifer_ and _ferox_ by a number of characters
(plastron and especially skull) whereas the species _spinifer_ and
_ferox_ are not easily distinguished from one another.
Composition of the Genus _Trionyx_ in North America
Analysis of the characters previously mentioned and their geographic
distribution permits the recognition of ten taxa, comprising four
species and eight subspecies. Two subspecies, _T. spinifer_ pallidus
and _T. s. guadalupensis_ are described as new. The four species and
the included subspecies here recognized are:
_Trionyx ferox_
_Trionyx spinifer spinifer_
_hartwegi_
_asper_
_emoryi_
_guadalupensis_
_pallidus_
_Trionyx ater_
_Trionyx muticus muticus_
_calvatus_
The following key is designed to permit quick identification of living
individuals; therefore, ratios and osteological characters are avoided
as much as possible in favor of other characters that are the least
variable and most "typical." Because there is considerable variation
correlated with sex and size, each taxon occurs in the key in more
than one couplet. Large females having mottled and blotched patterns
will be the most difficult to identify. The characters listed should
be used in combination because one character alone may not be
sufficient; it is advisable to read both choices of each couplet. The
text, figures and illustrations should be consulted for final
identification.
ARTIFICIAL KEY TO NORTH AMERICAN SPECIES AND SUBSPECIES OF THE GENUS
TRIONYX
1. Septal ridges present; tubercles on anterior edge of
carapace present or absent 2
Septal ridges absent; anterior edge of carapace lacking
tubercles or raised prominences 19
2. Plastral area a uniform dark slate or blackish; soft
parts of body blackish having large pale marks dorsally;
carapace having large black blotches, often fused along
margin, on pale background, and many well-defined
longitudinal ridges _ T. ferox_, p. 479
Combination of characters not as above; ventral
surface whitish, blackish flecks or blotches
sometimes present 3
3. Carapace having pattern of white dots, or black ocelli
and/or spots; carapace sometimes gritty resembling
sandpaper 4
Carapace uniform pale brownish or grayish, or having
mottled and blotched pattern, contrasting or not; white
dots or tubercles, black ocelli and/or spots may be
present; carapace not gritty 10
4. Carapace having pattern of black ocelli and/or spots;
numerous, conspicuous whitish spots or tubercles absent 5
Carapace having pattern of white dots that are sometimes
surrounded by small black ocelli; small black dots may be
interspersed among larger white dots 7
5. Carapace having two or more marginal lines, these often
diffuse and interrupted; black spots sometimes ocellate
or bacilliform, or interspersed among smaller black dots;
postocular and postlabial stripes usually united
_spinifer asper_, p. 502
Carapace having only one dark marginal line; pattern of
black ocelli or spots; postocular and postlabial stripes
usually not united 6
6. Carapace having prominent ocelli, which are much larger
near the center than at the sides
_spinifer spinifer_, p. 489
Carapace having numerous small, dark spots, sometimes
small ocelli, which are not much larger near the center
than the sides _spinifer hartwegi_, p. 497
7. White spots on anterior third of carapace; white spots
on carapace often surrounded by narrow blackish ocelli;
small black dots sometimes interspersed among white spots
_spinifer guadalupensis_, p. 517
White spots absent on anterior third of carapace, or
small and inconspicuous; white spots not surrounded
by narrow blackish ocelli 8
8. Pale rim of carapace narrow, partly obscured; over-all
dorsal coloration (including soft parts of body) dark and
lacking pattern; few, small, white tubercles confined to
posterior third of carapace _ater_, p. 528
Pale rim distinct, without markings; soft parts of body
dorsally not uniformly dark; many white tubercles
usually contrasting on pale carapace 9
9. White spots confined to posterior third of carapace;
ground color of carapace usually pale brown or tan,
sometimes darker; a dark, slightly curved, line
connecting anterior margins of orbits; postocular stripe
usually interrupted leaving pale, blotch behind eye;
pale rim of carapace four or five times wider
posteriorly than laterally _spinifer emoryi_, p. 510
Small white spots on posterior half of carapace gradually
decreasing in size anteriorly, often indistinct or absent
on anterior third of carapace; pale rim of carapace no
more than three times wider posteriorly than laterally
_spinifer pallidus_, p. 522
10. Marginal ridge present; carapace having ill-defined
dark blotches on uniform grayish, lacking whitish
tubercles or well-defined black spots or ocelli; pale
rim of carapace absent; tubercles on anterior edge of
carapace resembling flattened hemispheres; anterior
parts of plastron often visible in dorsal view;
postocular stripe, if present, having thick, blackish
borders _ferox_, p. 479
Marginal ridge absent 11
11. Carapace uniform pale brownish, lacking mottled and
blotched pattern, white dots, black ocelli or spots 12
Carapace having mottled and blotched pattern,
contrasting or not; white spots or tubercles, black
ocelli or spots may be present 13
12. Pale rim of carapace four or five times wider
posteriorly than laterally; dark, straight or slightly
curved, line connecting anterior margins of orbits
_spinifer emoryi_, p. 510
Pale rim of carapace no more than three times wider
posteriorly than laterally _spinifer pallidus_, p. 522
13. Rear margin of carapace usually roughened by fine
corrugations, edge often ragged; pale rim absent;
carapace having dark brown-blackish, mottled and
blotched pattern; anterior edge of carapace more or
less smooth having scarcely elevated prominences;
posterior part of plastral area and especially ventral
surface of carapace having numerous black marks
_ater_, p. 528
Rear margin of carapace smooth, edge entire;
usually some evidence of pale rim 14
14. White, rounded tubercles or spots usually evident
posteriorly on carapace, sometimes indistinct; black
ocelli or spots lacking in center of carapace,
sometimes present at sides; shape of tubercles on
anterior edge of carapace variable 15
White spots or tubercles absent; margin of carapace
usually having black ocelli or spots; tubercles on
anterior edge of carapace equilateral or conical,
not low and flattened 17
15. White spots often present on anterior half of carapace;
tubercles on anterior edge equilateral and wartlike,
or less elevated, not conical
_spinifer guadalupensis_, p. 517
White spots usually absent on anterior half of
carapace, sometimes indistinct; shape of tubercles
on anterior edge of carapace variable 16
16. White spots absent on anterior half of carapace;
tubercles on anterior edge of carapace low, scarcely
elevated, never equilateral or conical; mottled and
blotched pattern often not contrasting; ground color of
carapace sometimes dark; pale rim of carapace four or
five times wider posteriorly than laterally; dark,
straight or slightly curved, line connecting anterior
margins or orbits _spinifer emoryi_, p. 510
White spots sometimes indistinct on carapace, or few,
small spots present on posterior half of carapace;
tubercles on anterior edge of carapace equilateral and
wartlike or conical; mottled and blotched pattern usually
contrasting; pale rim less than three times wider
posteriorly than laterally _spinifer pallidus_, p. 522
17. Carapace having evidence of more than one dark marginal
line, and scattered, black spots or ocelli
_spinifer asper_, p. 502
Carapace having only one, dark, marginal line 18
18. Carapace having small black spots, lacking large
interrupted ocelli _spinifer hartwegi_, p. 497
Carapace having small black spots interspersed among
larger, interrupted ocelli _spinifer spinifer_, p. 489
19. Carapace having pattern of dusky spots, sometimes
short lines 20
Carapace lacking pattern of dark spots or lines,
having a mottled and blotched pattern 21
20. Pattern of circular spots, lacking short lines or
bacilliform marks; spots sometimes slightly ocellate;
no pale stripes on snout _muticus calvatus_, p. 539
Pattern of dots, or dots and short lines; pale
stripes on snout, at least just in front of eyes
_muticus muticus_, p. 534
21. Mottled and blotched pattern usually contrasting;
ill-defined, blackish blotch absent behind eye
_muticus muticus_, p. 534
Mottled and blotched pattern usually not contrasting;
ill-defined, dark blotch may be present behind eye
_muticus calvatus_, p. 539
Systematic Account of Species and Subspecies
=Trionyx ferox= (Schneider)
Florida Softshell
Plates 31 and 32
_Testudo ferox_ Schneider, Naturg. Schildkr., p. 330, 1783 (based
on Pennant, Philos. Trans. London, 61 (Pt. 1, Art. 32): 268,
pl. 10 [figs. 1-3], 1772).
_Trionyx ferox_ Schwartz, Charleston Mus. Leaflet, No. 26:17,
pls. 1-3, May, 1956.
_Testudo mollis_ Lacépède, Hist., Nat. Quadr. Ovip. Serp., 1:137,
pl. 7, 1788.
_Testudo_ (_ferox_?) verrucosa Schoepff, Hist. Testud., Fasc. 5
(Plag. M):90, pl. 19, 1795.
_Testudo bartrami_ Daudin, Hist. Nat. Rept., 2:74, pl. 18, fig. 2,
1801.
_Trionyx georgicus_ Geoffroy, Ann. Mus. Hist. Nat., Paris, 14:17,
August, 1809.
_Mesodeca bartrami_ Rafinesque, Atlan. Jour., Friend Knowledge,
Philadelphia, 1 (No. 2, Art. 12):64, Summer, 1832.
_Trionyx harlani_ Bell in Harlan, Medic. Phys. Research, p. 159,
1835.
_Type._--Holotype, British Museum (Natural History) 1947.3.6.17; original
number 53A, presumably that of Royal Society; stuffed adult female and skull;
obtained from the Savannah River, Georgia, by Dr. Alexander Garden.
_Range._--Southern South Carolina, southeastern Georgia, and all of Florida
except the Keys and perhaps the western end of the panhandle (see map, Fig.
18).
[Illustration: FIG. 18. Map of southeastern United States showing geographic distribution
of _Trionyx ferox_.]
_Diagnosis._--Marginal ridge present; longitudinal rows of tubercles that
resemble ridges on carapace of hatchlings; plastron often extending farther
forward than carapace in adults; plastral area dark slate or gray in hatchlings;
juvenal pattern of large slate or blackish blotches (often with pale centers)
on a pale background; pale outer rim of carapace (absent on adults) narrow,
not separated from ground color of carapace by distinct, dark line.
Size large; head wide; carapace relatively long and narrow; snout short;
greatest width of skull at level of quadratojugal; often no suture between
hypoplastra and hyoplastra; callosities on epiplastron and preplastra usually
lacking.
_Description._--Plastral length of smallest hatchling, 2.9 centimeters (UMMZ
95613), of largest male, 26.0 centimeters (AMNH 63642), of largest female,
34.0 centimeters (UMMZ 38123).
Septal ridges present; over-all coloration of carapace and plastron, and soft
parts of body of hatchlings slate or blackish; carapace having blackish, circular
blotches, usually fused at margin, often with pale centers on buff background
forming coarse reticulum; pale, narrow rim of carapace not separated from
ground color by dark marginal line; pale rim, coincident with marginal ridge,
absent from anteriormost nuchal region; longitudinal rows of tubercles on
carapace resembling ridges; undersurface blackish, usually having posterior part
of carapace pale with irregular blackish marks; blackish soft parts of body
dorsally having large, pale markings, most consistent of which are postocular
mark that may contact orbit, postlabial mark that curves around angle of jaws,
inverted Y on top of snout, and one or two streaks on side of neck.
Over-all coloration of adults grayish, paler than in hatchlings; carapace gray
sometimes having slightly darker, large, irregular markings; mottled and
blotched pattern on females not contrasting; sex of many large individuals not
distinguishable on basis of pattern on carapace; pale rim of carapace obscure or
absent; soft parts of body dorsally gray or brownish on large adults of both
sexes, sometimes having slightly paler, large markings; small adult males usually
having contrasting pattern on head; surface of carapace smooth (not "sandpaper")
on adult males; undersurface whitish, throat often grayish; well-defined
marginal ridge; anterior edge of carapace laterally to region of insertion
of forelimbs studded with low, flattened tubercles resembling hemispheres, never
conical; carapace usually having blunted tubercles, best developed anteriorly
and posteriorly on midline, but sometimes linearly arranged, resembling ridges,
especially at margins; anterolateral parts of plastron often extending farther
forward than corresponding parts of carapace.
Range in length (in cm.) of plastron of ten largest specimens of each sex
(mean follows extremes), males, 17.0-26.0, 20.0; females 23.3-34.0, 27.9;
ontogenetic variation in PL/HW, mean PL/HW of specimens having plastral
lengths 6.5 centimeters or less, 3.52, and exceeding 6.5 centimeters, 4.87;
ontogenetic variation in CL/CW, mean CL/CW of specimens having plastral
lengths 8.0 centimeters or less, 1.18, and exceeding 8.0 centimeters, 1.30; mean
CL/PCW, 2.01; mean HW/SL, 1.44; mean CL/PL, 1.26.
Jaws of some skulls that exceed 75 millimeters in basicranial length having
expanded alveolar surfaces; greatest width of skull usually at level of quadratojugal
(72%); ventral surface of supraoccipital spine narrow proximally, usually
having medial ridge; foramen magnum rhomboidal; opisthotic-exoccipital spur
absent (82%), sometimes indicated by ridge (16%); distal part of opisthotic wing
tapered, not visible in dorsal view; lateral condyle of articular surface of quadrate
larger than medial articular surface, not tapered posteriorly; maxillaries in contact
above premaxillaries; usually a combination of seven neurals, seven pairs
of pleurals, and contact of seventh pair of pleurals (56%), often eight pairs of
pleurals (31%); angle of epiplastron forming approximate right angle; often no
suture between hypoplastra and hyoplastra; callosities on preplastra and epiplastron
usually lacking.
_Variation._--Crenshaw and Hopkins (1955:19) stated that in specimens from
Lake Okeechobee and southward the carapace is wider relative to the width of
the head, and Neill (1951:19) quoted Allen's observations that _ferox_ from southern
Florida "average larger and darker than those collected farther north."
Carr (1952:417) reported that the pale reticulum on the carapace is yellowish
olive, the markings on head are yellow on an olive ground color, some
markings more orange, and the plastron slate gray. Duellman and Schwartz
(1958:271) mentioned that the carapace of hatchlings is edged in orange
grading to yellow posteriorly and has a pattern of bluish-black blotches on a
dull brown background, whereas the carapace is dull brown or blackish on
adults. Neill (_op. cit._:18) wrote "that the head stripes and the marginal
ring of the 'carapace' are orange rather than yellow (yellow at the time of
hatching, however)."
The transition from the dark coloration of hatchlings to the paler coloration
of adults is gradual and subject to individual variation. The loss of
dark color ventrally occurs first on the plastral area, then the hind limbs, forelimbs,
posterior part of carapace and last on the neck and throat. The soft
parts of the body dorsally are gray or dark gray, and do not become so pale
as the ventral surface. The smallest specimen that I have seen displaying the
dark features of the hatchlings is a male, 7.7 centimeters (UMMZ 100673);
a female, 9.5 centimeters (UMMZ 110987), is the smallest specimen having
a whitish plastral area. The change from dark to pale coloration on the ventral
surface occurs at a size of 8.0 to 9.0 centimeters. The largest specimens I
have seen having indistinct, dusky blotches of the underside of the carapace
are a female, 11.3 centimeters (UMMZ 100836), and a male, 16.0 centimeters
(UMMZ 106322). A contrasting pattern on head and limbs, and a
dark throat are still evident in a female 19.2 centimeters (UMMZ 106302).
_Comparisons._--_Trionyx ferox_ can be distinguished from all other species
of the genus in North America by the presence of a marginal ridge, longitudinal
ridges of tubercles on the carapace of juveniles (less evident in adults),
and the unique juvenal pattern and coloration. The lack of a juvenal pattern
and a smooth surface on the carapace (not gritty like sandpaper) distinguish
adult males from those of _T. spinifer_. Most adults of both sexes can be distinguished
from _spinifer_ and _muticus_ by the extension of the plastron farther
forward than the carapace (developed to a slight degree in some specimens
of _T. s. emoryi_). Both sexes of all ages can be distinguished from _muticus_ by
the presence of knoblike tubercles on the anterior edge of the carapace, and
septal ridges.
_T. ferox_ is the largest species in North America; the maximum size of the
plastron in adult males is approximately 26.0 centimeters (16.0 in _spinifer_)
and of adult females, 34.0 centimeters (31.0 in _spinifer_). The head is wider
in _ferox_ than in _muticus_ and most subspecies of _spinifer_ (closely approached
by _asper_, _guadalupensis_, _emoryi_ and _T. ater_). The carapace is narrower in
_ferox_ than in _muticus_ and most subspecies of _spinifer_ (closely approached by
_emoryi_ and _T. ater_). The snout is shortest in _ferox_, but almost as short in
_T. s. emoryi_ and _T. ater_. _T. ferox_ has proportionately the longest plastron in
relation to length of carapace.
Most skulls of _ferox_ differ from those of _muticus_ and _spinifer_ in having the
greatest width at the level of the quadratojugal (as do some _T. s. asper_; see
account of that subspecies). In the skull, _ferox_ resembles _spinifer_ but differs
from _muticus_ in having the 1) ventral surface of the supraoccipital spine narrow
proximally, and usually having a medial ridge, 2) foramen magnum rhomboidal,
3) distal part of opisthotic wing tapered, 4) lateral condyle of articular
surface of quadrate not tapered posteriorly, and larger than medial articular
surface, and 5) maxillaries in contact above premaxillaries. _T. ferox_ resembles
_muticus_ but differs from most individuals of _spinifer_ in lacking a well-developed
opisthotic-exoccipital spur. _T. ferox_ resembles _spinifer_ but differs from
_muticus_ in having the epiplastron bent at approximately a right angle; _ferox_
differs from both _muticus_ and _spinifer_ in lacking a callosity on the epiplastron
and probably in the more frequent fusion of the hyoplastra and hypoplastra.