BULLETIN FLORIDA STATE MUSEUM


mesotyle are well developed; the metastyle is not so well developed.
The anterior and posterior borders of the pre- and post-fossettes are
moderately plicated, whereas the external and internal borders are
relatively simple. The plicaballin is usually represented by a single
loop, but in a few specimens this structure is absent. The protocone is
oval or bean-shaped and does not exhibit the angular character seen in
"Nannippus" lenticularis. The protocone is united with the protoloph
in late wear stages. The hypoconal groove varies progressively from
moderately developed during early and middle wear stages to absent
during late wear stages.
 The mandible has an elongate symphysis (Fig. 4.) in contrast to
other small "Hipparion"-like horses such as Calippus and Pseudhip-
parion. The lower incisors have cement-filled infundibula not recessed
below the occlusal surface. The incisor series is curved and relatively
procumbent (or spatulate). The precanine diastema is very short in
relation to the postcanine diastema. The mental foramen is approx-
imately midway between C and P,. P1 is absent.
 The lower molars are moderately curved in the anteroposterior
plane and slightly curved in the transverse plane. The lower deciduous
premolars, e. g. UF 21319 and UF 21320 (almost certainly from the
same individual), are more elongate anteroposteriorly and narrower
transversely than are the permanent premolars and molars (Fig. 5,
Tables 3, 4). The protoconids and hypoconids have flattened external
borders and are narrow transversely. The ectoflexid is relatively
shallow. The metaconids and metastylids are anteroposteriorly
elongated (transversely compressed) and are widely separated. The en-
toconid is much larger than the hypoconulid. These two parts are
distinct and widely separated. The enamel foldings are simple except
for some plications on the anterointernal border of the hypoconid. In
summary, the individual teeth, as well as the constituent parts, such
as conids, lophids, and stylids, are anteroposteriorly more elongate in
the deciduous dentition than in the permanent dentition. The elongate
character of the deciduous dental row (both lower and upper), which is
characteristic of horses in general, is related to a maximum occlusal
surface needed during early growth stages after weaning. The lower
deciduous dentition from Florida is similar to that of Nannippus
phlegon from Mt. Blanco (e.g. AMNH 104710), although the former
has a thinner investment of cement.
 In cross-section the lower permanent premolars and molars are
longer than wide (Figs. 4,6,7). The paralophid is slightly expanded
anteriorly in P2, but much less so than in most hipparions. The exter-
nal borders of the protoconids and hypoconids are rounded. The ec-
toflexid varies (either within an individual tooth row or with pro-


Vol. 25, No. 1