PAL^EOSYOPS LEIDY, AND ITS ALLIES. 
381 
ectocuneiform is high and narrow and is characteristic of this group. We have 
seen that in this subfamily the reverse type of tarsal articulation never occurs. 
In the following tables I have arranged the primitive and specialized charac- 
ters occurring in this group in columns, but no one species contains all primitive 
characters. The dentition, for example, maybe highly specialized while the carpus 
or tarsus may not have undergone as much disjilacement as in another fonn 
where the dentition is more primitive. 
Primitive Characters. 
1. Incisors without strong basal cingula. 
2. Canines rather short and stout with- 
out cutting edges. 
3. Superior premolar 1 a cone without 
prominent heel; inferior premolar 1 
also simple. 
4. Superior premolar 2 with only one 
external lobe and with internal lobe 
wanting. Inferior premolar 2 with 
lobes subequal. 
5. Inferior premolar 3 without a meta- 
conid. 
6. Superior premolar 4 with transverse 
diameter much less than that of 
molar 1, also with external lobes not 
separated b}^ a buttress. Inferior 
premolar 4 with V’s not strongly 
expressed. 
7. Crowns of molars strongly brachy- 
dont with external V’s rounded, nar- 
row and with a median rib present. 
Median buttress not constricted off' 
and wAth anterior buttress strongly 
prolonged. Lower molars with crests 
of V’s not prominent. Last inferior 
molar with its posterior tubercle a 
functional lobe. 
8. Intermediate tubercles of premolars 
and molars large and, in the most 
primitive form, with protoconule and 
metaconule present on upper true 
molars (^Limnohyops) . 
Progressive Characters. 
1. Incisors with strong ba.sal cingula. 
Posterior face of incisors vertical. 
2. Canines elongated, slender and with 
sharj) cutting edges. 
3. Superior premolar 1 elongated, with 
anterior and posterior tuliercles. 
4. Superior premolar 2 with two well 
develojied external IoIk's. Internal 
lobe of same present, .\nterior 
lobe of inferior preinolar 2 much 
larger than posterior. 
5. Inferior preiuolar 3 with a inetaconid 
{Lambdothcriuni) . 
G. Sujierior premolar 4 with transverse 
diameter nearly eipial to that of 
molar 1. E.xternal lobes of preinolar 
4 separated by a buttivss. In- 
ferior preinolar 4 with I”8 well de- 
veloped but without an entocunid. 
7. Crowns of molars liigli, with external 
V’s very broad and angular. Median 
rib of same absent. Median buttress 
strongly constricted oil. .Interior 
buttress not widely pnilonged. Crests 
of lower molars very high and sharp. 
Last inferior molar with jMisterior 
tubercle specialized in the form of 
a cone without cifsts and valley. 
8. Intermediate tulx*rcles of su|x’rior 
premolars and molars much n*duced. 
9. Last superior molar with only one 
internal cone. 
