Nerodia Baird and Girard 1853

Genus NERODIA Baird and Girard, 1853 Diagnosis. The trunk vertebrae of Nerodia are typically medium to large in size and relatively short and wide, with an elongate centrum (Holman, 2000). The neural spines and hypapophyses are prominent (Holman, 2000). The neural spine is tall and undercut on both the anterior and posterior sides. The robust hypapophyses on each precaudal vertebra are well-developed, laterally compressed, directed posteriorly, and usually end in a somewhat pointed tip extending beyond the condylar head (Holman, 2000). Epizygapophyseal spines are absent (Holman, 2000). Remarks. The trunk vertebrae of Nerodia relative to other North American natricids are typically medium to large in size, relatively robust in appearance, and exhibit higher neural spines (Holman, 2000). The vertebrae are still elongate relative to large North American colubrines (Holman, 2000). Nerodia vertebrae are typically less elongate than Thamnophis vertebrae, with a more ventrally-oriented hypapophysis with a steeper angle relative to the centrum (LaDuke, 1991; Holman, 2000; Jasinski and Moscata, 2017). Nerodia also exhibits a more vaulted neural arch, broader and more robust hypapophyses, but more gracile prezygapophyses compared to Thamnophis (Jasinski and Moscato, 2017). They possess higher neural spines than Storeria, Tropidoclonion, and Virginia (but relatively shorter than Regina), and the hypapophyses are longer and less squared in shape when compared to Regina (Holman, 2000). It should be noted that the degree to which the hypapophysis extends beyond the condylar head appears to differ between some taxa, and perhaps between individuals, though this has not been extensively studied at this time. Other characters of Nerodia, such as neural spine height, hypapophysis shape, and the degree to which the neural spine is undercut all vary to some degree at least between species of the genus (Holman, 2000; pers. obs.).