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).
I have seen only three specimens from the Colorado River drainage in Texas. Two of these (UMMZ 92751, TU 14436) are characterized by much black pigmentation. A contrasting pattern of relatively large black marks occurs on the dorsal surface of the soft parts of the body, especially on the [536] hind limbs, and the pale postocular stripes have thick black borders. UMMZ 92751, having a plastral length of 5.5 centimeters, has a juvenal pattern of widely-spaced dark dots that lacks short lines. The other muticus from the Colorado River (CM 3055), a large female 19.0 centimeters in plastral length, has ill-defined postocular stripes lacking dark borders, although a small dusky blotch occurs on the right side of the head.
Comparisons.—T. m. muticus differs from T. m. calvatus in having pale stripes on the snout, a juvenal pattern of small dusky spots (usually lacking ocellate spots) and short lines, and a pale postocular stripe lacking thick, blackish borders (except in some turtles from the Colorado River system of Texas). One unique characteristic of muticus is the short, dusky lines in the juvenal pattern; these marks, however, are occasionally absent.
Remarks.—Trionyx muticus generally has been considered a distinct species since its description by Lesueur (1827:263-66, Pl. 7); Wied-Neuwied (1865:53), at least, questioned the identity of muticus, believing it to be based on a secondary sexual difference of T. spiniferus. Lesueur did not designate a type in the description, and mentioned that he had seen only three specimens (op. cit.:264). Stejneger (1944:17-18) discussed two mounted specimens (Nos. 787 and 788) in the Natural History Museum at Paris, and mentioned that No. 787 was designated "… as the type on the printed label (although presumably not done by Lesueur)." Dr. Jean Guibé (in litt. September 24, 1959) informed me that Nos. 787 and 788 are numbers without value and correspond, respectively, to catalog numbers 8813 and 8814. In addition, the Museum possesses an alcoholic specimen, No. 564, obtained by Lesueur from the Wabash River, that seems to have been acquired by the museum after the publication of the original description. No. 8813 is regarded as a lectotype.
Gray (1864:87) described the species microcephalus and questionably included it in the genus Potamochelys Fitzinger, 1843; the locality was stated as "Sarawak (Wallace)." Gray especially noted the small elongate head and believed that the acquisition of adult specimens would prove that it belonged to a new genus. Later, Gray (1869:221) proposed the generic name Callinia as a new name for Aspidonectes as understood by Agassiz (1857:403). Gray referred microcephala to Callinia (op. cit.:214, 222) and recognized also Amyda mutica (op. cit.:212). Baur (1888:1121) remarked that "Callinia microcephala Gray, of the British Museum, with the locality Sarawak, is Amyda mutica Les." The species microcephalus has since been considered a synonym of Trionyx muticus. Schmidt (1953:110) designated the type locality as New Harmony, Indiana.
Müller (1878:641) listed the species Trionyx muticus from México as follows: "*b. in Alcohol. Mexico. 1872. [2]." Smith and Taylor (1950:18, footnote) wrote that the record required confirmation. Webb and Legler (1960:24) questionably referred this record to the synonomy of T. ater, which resembles muticus. T. muticus is not known to occur in México. According to Dr. Lothar Forcart (in litt.) of the Naturhistorische Museum in Basel, Switzerland, only one specimen on which Müller based his record is extant. My examination of this specimen reveals that it is a hatchling T. s. emoryi, plastral length 3.5 centimeters, bearing catalog number 1032; there are no additional data of collection.
Strecker and Williams (1927:16) mentioned one specimen of muticus that was obtained at Christoval, Tom Green County, Texas, and I presume this is the basis for Pope's mention of this species from Tom Green County, Texas (1949:319). Although I do not doubt that T. muticus occurs in Tom Green County, this record possibly is based on T. spinifer because, 1) there are no specimens of muticus in the Strecker Museum from Tom Green County, but there is one specimen of spinifer (SM 3282), and in none of Strecker's publications is there any mention of spinifer from Tom Green County, and 2) Strecker had, at least once, misidentified the two species; his record of muticus from Wallace Bayou, Louisiana (Strecker and Frierson, 1926:last page, no numbers), represents T. spinifer pallidus (SM 2374-75).
Specimens examined.—Total 261, as follows: Alabama: County unknown: USNM 118167, Wheeler Reservoir, Tennessee River.