Table 10 is the resemblance of _ferox_ to _T. muticus calvatus_ in having thick, black-bordered postocular stripes. Some populations of _T. s. emoryi_ resemble _T. muticus_ in the corresponding size at sexual maturity and in having well-developed plastral callosities. It is notable that the occurrence of _ater_, and to a lesser extent that of _T. s. emoryi_, which resembles _ferox_ (and _muticus_), is in the southwestern United States and northern México. TABLE 10. Frequency of Selected Characters Among Species and Subspecies of Trionyx in North America. Characters of muticus Refer to the Typical Subspecies; Horizontal Dashes Connecting X's Indicate that Computations for Those Subspecies Were Combined; Vertical Dashes Indicate that the Subspecies Is Intermediate Between the Adjacent Subspecies. Column headings: A: _ferox_ B: _spinifer_ C: _hartwegi_ D: _asper_ E: _pallidus_ F: _guadalupensis_ G: _emoryi_ H: _ater_ I: _muticus_ =====================================+=================================== | Species and subspecies Characters +---+---+---+---+---+---+---+---+--- | A | B | C | D | E | F | G | H | I -------------------------------------+---+---+---+---+---+---+---+---+--- Juvenal pattern: | | | | | | | | | black spots, ocelli | | X | X | X | | | | | | | | | | | | | | white dots | | | | | X | X | X | X | -------------------------------------+---+---+---+---+---+---+---+---+--- Pattern on snout: | | | | | | | | | acute angle (reduced in _muticus_) | X | X | X | X | X | | | | X | | | | | ¦ | | | | triangular | | | | | X | X | X | X | -------------------------------------+---+---+---+---+---+---+---+---+--- Pattern on side of head: | | | | | | | | | contrasting marks | X | X | X | X | X | X | | | | | | | | | ¦ | | | non-contrasting marks (distinct | | | | | | ¦ | | | stripe in _muticus_) | | | | | | X | X | X | X -------------------------------------+---+---+---+---+---+---+---+---+--- Pattern on limbs of adults: | | | | | | | | | contrasting | | X | X | X | X | X | | | | | | | | | ¦ | | | reduced or absent | X | | | | | X | X | X | X -------------------------------------+---+---+---+---+---+---+---+---+--- Tuberculation (anterior edge of | | | | | | | | |