Presence or absence of areolae on laminae of the shell indicated
degree and sequence of wear. The anterior edges of carapace and
plastron, and the slightly elevated middorsal line (Pl. 23) wear
smooth in some individuals before the first period of hibernation.
Subsequent wear on the carapace proceeds posteriorly. For example,
turtles that retained the areola of the third central lamina, retained
also the areolae of the fourth and fifth centrals; when only one
central areola remained, it was the fifth. Lateral laminae wear in the
same general sequence. The areola of the fifth central lamina, because
of its protected position, persists in adult turtles that are well
past the age of regular growth. Areolae that are retained in some
older turtles are shed along with the epidermal layers formed in the
first year or two of life. Wear on the shell is probably correlated
with the habits of the individual turtle; smoothly-worn specimens
varied in size and age but were usually larger, older individuals. No
smoothly worn individual was still growing.
Wear on the plastron is more evenly distributed than wear on the
carapace; wear is greatest on the lowest points of the plastron (the
gular laminae, the anterior portions of the anal laminae, and the
lateral edge of the tranverse hinge).
The claws and the horny covering of the jaws are subject to greater
wear than any other part of the epidermis; presumably they continue to
grow throughout life. The occasional examples of hypertrophied beaks
and claws that were observed, chiefly in juveniles, were thought to
result from a continuous diet of soft food or prolonged activity on a
soft substrate. Ditmars (1934:44, Fig. 41) illustrated a specimen of
_T. carolina_, with hypertrophied maxillary beak and abnormally
elongate claws, that had been kept in a house for 27 years.
The conformation of the maxillary beak in all species of _Terrapene_
is influenced to a large extent by wear and is of limited value as a
taxonomic character. The beak of _T. ornata_ is slightly notched in
most individuals at the time of hatching and remains so throughout
life. The underlying premaxillary bone is always notched or
bicuspidate. The sides of the beak are more heavily developed than the
relatively thin central part. Normal wear on the beak maintains the
notch (or deepens it) in the form of an inverted U or V, much in the
manner of the bicrenate cutting edge on the grooved incisors of
certain rodents. In a series of 34 specimens of _T. ornata_ from
Kansas, selected at random from the K. U. collections, 92 per cent had
beaks that were "notched" to varying degrees, four per cent had hooked
(unnotched) beaks, and four per cent had beaks that were flat at the
tip (neither hooked nor notched).
[Illustration: FIG. 21. Plantar views of right hind foot (male
at left, female at right) of _T. o. ornata_ (A-- 1), showing
sexual dimorphism in the shape and position of the first toe.
The widened, thickened, and inturned terminal phalanx on the
first toe of the male is used to grasp the female before and
during coitus.]