Smith (1956:159), referring to _muticus_, wrote that they are the best swimmers of all fresh-water turtles, and perhaps of any turtles. Corresponding statements of other authors attesting to their speed and agility (including _spinifer_ and _ferox_) in water and on land are based principally on the published comments of Muller (1921:181), who observed that females disturbed while laying eggs "about fifty feet from water ... covered the distance faster than a man can run." Cahn (1937:180) also stated that _muticus_ on a "level, unobstructed sand beach ... can outrun a man," and (_op. cit._:181) can "capture fish with ease"; Cahn supported the latter statement by relating his observation of a _muticus_ that captured a small brook trout in a large tank. Smith (_op. cit._:162) wrote that _spinifer_ is "said to overtake bass." Doubtless they are good swimmers and they do scurry rapidly on land. Published statements relating to the strictly aquatic existence of softshells especially _muticus_, are based on recognition of "its drastic adaptations to aquatic existence" (Carr, 1952:428); these adaptations presumably include pharyngeal respiration and the marked depression of body form. Pharyngeal respiration was demonstrated for _muticus_ and _spinifer_ (Gage, 1884; Gage and Gage, 1886), and was considered the principal type of aquatic respiration (some dermal and some cloacal) in _Trionyx spinifer asper_ by Dunson (1960). Cloacal bursae (anal respiration) are lacking in trionychids (Smith and James, 1955:88). Accessory pharyngeal respiration is meaningful in light of the information furnished by Agassiz (1857:282-83), who found that _Trionyx_ has a smaller lung capacity (weight of body in ounces/capacity of lungs in cubic inches = 16.9) than do some other genera (_Pseudemys_, 2.8; _Testudo_, 2.7; _Terrapene_, 1.1); corresponding values for more aquatic species were _Chelydra_, 9.3 and _Kinosternon_, 16.0. Cahn (1937:181), however, wrote that he has demonstrated pharyngeal respiration in individuals of _Pseudemys_, _Chrysemys_ and _Sternothaerus_, and Allen and Neill (1950:13) suggested that it occurs in _Macroclemys_. More conclusive data are required to detect a positive correlation between small lung capacity, pharyngeal respiration, and degree of restriction to an aquatic habitat.