1.08 
ON SOME AND LITTLE KNOWN OJiEODONTS. 
tion is not quite like tlie molars in pattoru, but altogether like the 4th premolar of 
PacJuj,Huf (3) the last molar of Mesonyx is very different from the 3rd molar of 
Puchyana'-miX entirely like the 2iid molar. It seems reasonable therefore to infer 
that the missing tooth in Mesonyx is the 3rd molar. This 4th premolar, as I shall 
call it, re.sembles the molars in having a large internal cusp, but differs from them in 
the conformation of the outer part of the croivn, which is not so plainly divisible 
into two cusps ; the cingulum is confined to the outer face of the crown. The molars 
are es.sentially alike, though the first has a somewhat greater antero-posterior and pro- 
portionately smaller transierse diameter; there are two external cusps, with a cingu- 
lum on the outer side, and anterior and posterior basal tubercles (the posterior is not 
jiresent on the 2nd molar) ; the internal cusp is very large and placed opposite the 
antero-external one. 
Ixm-er Jan:. Tlie incisors are A ery small and simple with compressed fangs and 
without cingulum. Tlie canine is bear-like and is somewhat ev erted. The 1st pre- 
molar is missing from the specimen ; the 2nd has tAvo fangs, a small conical croAvn 
Avith rudimentary heel. The 3rd and 4th are essentially like the molars, consisting of 
a thick retroverted conical cusp and lieaA y blade-like heel ; the anterior basal tuber- 
cle apiiears only on the 4th. The molars decrease in size posteriorly ; the main cu.sp 
is larger and thicker than on the premolars ; on the 3rd molar the heel is much re- 
duced and the anterior basal tubercle rudimentary. These molars differ from those of 
Parhya tm in the much greater development of the heel and the reduction of the an- 
terior basid tubercle. In Pacliyama the tubercle and heel are about the same size, 
giving the tooth a very different appearance. (See Cope, PI. XX^TII h. Fig. 1). 
All the molars of Mesonyx are Avorn at the tips, so that they have become more and 
more blunted Avith advancing age. 
M. >J>insu1ens differs from M. lanins chiefly in the canines and incisors; the for- 
mer are much flattened and worn on the sides, the latter .seem to be entirelv absent 
from the lower jaw, though this is not certainly determined, the shape of tlie sym- 
physus IS also Aery different, and more perfect specimens than have yet been obtained 
Anil very probably necessitate the revival of the genus Synoplotherinm, which Pro- 
les.sor C'oiie considers a snionym of Mesonyx. 
iHE ^ EKTEBK.VI. CoLu.AfN.— The atlexs is remarkable for the smalhie.ss of thetrans- 
Aerse proce-ssc^s which are nearly straight in direction and produced very little behind 
emarldrVT for the vertebral artery and are deeply 
tvnica r " appearance very unlike that in the 
and itlrtelT TKyUeynus. The superior arch is broad, 
»rch i, rfcmlor Zi ,hc LXfe I'T ' 
nnltaltn- 1' J’I'-'T': i"'? " W. a strou, keel, 
