American mud turtles
The mud turtles are small to medium-sized (to 27 cm), aquatic New World turtles with elongated to oval carapaces having either three longitudinal keels, a single middorsal keel, or no keel at all. The carapace may be domed or flattened dorsally, and has a smooth to slightly serrated posterior rim. A cervical scute is present along with 11 marginal scutes on each side. There are only four to seven neural bones, allowing some of the posterior costals to meet at the midline. Ten peripheral bones occur on each side of the carapace. The plastron varies from relatively large and broad to rather narrow. It contains either two transverse movable hinges bordering the abdominal scute which allow the plastron to close upon the carapace. The hindlobe is usually longer than the forelobe, and it may or may not contain a shallow posterior notch. There is no entoplastron. Plastral scutes may be completely or almost completely cornified at the seams. Only one gular scute is present. The bridge normally contains an inguinal scute, but the axillary may be absent. The head is moderate to large, with a projecting snout and, usually, a hooked upper jaw. The temporal region is moderately emarginated. The maxilla contacts the quadratojugal, and its triturating surface lacks a ridge. No contact occurs between the squamosal and postorbital, and the quadrate does not enclose the stapes. A secondary palate is present. All toes are webbed.
Kinosternon ranges from Connecticut west to Nebraska, southward through the Great Plains, Mexico, and Central America to Ecuador, Peru, Bolivia, Brazil, and northern Argentina in South America. Sixteen species and 20 subspecies are recognized, but other variation occurs and probably several additional taxa will be described.
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