Nearly all gradations from a fully developed zygomatic arch to a greatly reduced arch can be observed in skulls of the various species of _Terrapene_ (Fig. 2) (Taylor, 1895:586, Figs. 2-7). The highest degree of reduction is achieved in _T. ornata_ and _T. klauberi_, both of which lack the quadratojugal bone and have no zygomatic arch whatever (except for an occasional, poorly defined anterior vestige formed by the postfrontal, the jugal, or both). Reduction of the zygoma clearly represents modification of a more generalized, complete arch. As yet there is no clear evidence that reduction of the zygomatic arch is of adaptive value. It is noteworthy, however, that similar reduction of the arch has occurred independently in a number of emyid and testudinid groups, nearly all of which have terrestrial or semiterrestrial habits. Although discussion of phyletic lines in _Terrapene_ is beyond the scope of this report, I tentatively suggest that reduced zygomatic arches have arisen independently in more than one group of _Terrapene_ and that similar reduction of the arch in two species of the genus does not necessarily indicate an especially close relationship of such species. In a recent survey of cloacal bursae in chelonians, Smith and James (1958:88) reported _T. ornata_ and _T. mexicana_ to be among the few emyids that lacked these structures; in the opinion of the authors (_op. cit._:94) cloacal bursae evolved in chelonians that required an accessory respiratory organ for long periods of quiescence (hibernation or aestivation) under water, and were secondarily lost in terrestrial forms that hibernated on land. The assumption is a reasonable one, at least in regard to emyids and testudinids. Lack of cloacal bursae in _T. ornata_ and in all testudinids, can be correlated with the completely terrestrial habits of those turtles. Cloacal bursae seem to be vestigial in the species of _Terrapene_ possessing them and to be of little or no use as respiratory structures (except perhaps in _T. coahuila_).