Ritgen, 1828
Pond turtles
Recognition
Clemmys is a genus of four small to medium-sized (to 23 cm) turtles that frequent aquatic, semi-aquatic, or, occasionally, terrestrial habitats in North America. Their carapace is low arched, smooth surfaced or sculptured with growth annuli, and serrated or not posteriorly. A median keel is present in two species, absent in the other two. The hexagonal neural bones are short sided anteriorly. The plastron is weakly buttressed and hingeless. Its entoplastron is crossed by the humero-pectoral seam. The skull is short, flattened to slightly convex dorsally, and has a complete temporal arch. Its pterygoid does not meet the basioccipital, but the angular bones touch Meckel's cartilage. The jugal is tapered to a point ventrally and does not touch the pterygoid. The frontal bone enters the orbit, and the maxilla forms part of the inferior temporal fossa. Orbito-nasal foramina are small; triturating surfaces narrow and ridgeless. The toes are webbed, and the dorsal surface of the head is covered with smooth skin.
Remark
Molecular studies by Bickham et al. (1996) indicate that the North American genus Clemmys as now known is probably polyphyletic, with the species insculpta and muhlenbergii forming one clade, guttata another widely separated monospecific one, and marmorata showing closer affinities to Emydoidea blandingii and Emys orbicularis that two the other "Clemmys". Should the genus be split, the name Clemmys would apply only to C. guttata, the type species of the genus. The oldest valid name applicable for the muhlenbergii-insculpta line would be Calemys Agassiz, 1857, of which muhlenbergii is the type species. Marmorata would either be assigned to the genus Emydoidea or have a new genus created for it, since there is no available generic name for it.
Species identification
Jump to the key: Page 356: Genus Clemmys