299 
PAL^OSYOPS LEIDY, AND ITS ALLIES. 
tyles. Palcsosyx)ps shows its close affinity to Diplacodon in the characters of its 
lumbar vertebrm, in the latter form the neural arch and postzygapophysis having 
the same form as in the posterior dorsal region of P. paludosus. We have seen that 
at the posterior part the axial skeleton in this species departs widely from that of 
Tafnrus and Rhinoceros-, that it has strong Equine characters in the form of its 
articular processes, and also in the character of the neural arch. Cope mentions the 
fact that the pre- and postzygapophyses in Plyrachyus embrace each other as in the 
Equidce, and the vertebrae are elongated and high as in Palceosyops. PalaotJierium 
also agrees with Palceosyops in the form of its lumbar vertebrae, as in the former 
genus the articular processes are placed vertically. Pdyracothernmi approaches 
Eqtms ill the form of the lumbar processes, as is shown in the following descrqi- 
tion by Cope : — " 
“ The remaining parts of the column (including dorsal and lumbar) show decided 
indications of Equine rather than Tapiroid affinity in two points ; these are, first, 
the absence of isolated interspinous foramina, and second, the narrow form and more 
revolute articular surfaces of the postzygapophyses. ” 
The large size of the metapojihysis is a peculiarity of Palceosyops as compared to 
recent Perissodactyles, as in Equus these processes are larger in the posterior dorsal 
than in the lumbar region. In the Tapir and Rhinoceros on the other hand they 
reach their greatest size in the lumbar region, but they are very small comparatively. 
Sacrtim, No. 10,245. — The sacrum in this species is very long and narrow com- 
pared with that of Rhinoceros. It is made up of four coalesced vertebrm. The 
diapophyses are very short and compressed, those of the second being the largest 
and offering a large fiat iliac surface. The diapophysis of the third sacral vertebra 
is also much flattened, so that the pelvis probably articulates with this vertebra. 
The intervertebral foramina are large. 
The first sacral vertebra shows a much raised prezygapophysis, and in fact the 
vertical height of this part of the sacrum is greater than that of the Rhinoceros. 
The sacral diapophyses in this species have no articular surfaces for the lumbar 
vertebra} as they have in the Rhinoceros and TajDir. The extremely small size of 
the posterior face of the last sacral vertebra indicates that the tail was very short in 
this species, much more so than in Rhinoceros, where the body of the last sacral 
vertebra is quite large and broad. 
The Ribs. — There are a number of 2 }ortions of ribs in the collection. No. 10,281, 
all from the same individual, and as they are associated with the series of dorsal 
vertebrre which we have already described, I shall refer them to this species. The 
ribs are proj)ortionately longer and narrower than in the Rhinoceros, and the width 
of their shafts is intermediate between those of the Rhinoceros and the Tapir. The 
shaft is characterized Ijy its comparative thickness, and also by its external face being 
^Tertiary V6rtGbrata. Page 627. 
40 JOUR. A. X. S. PHILA., VOU. IX. 
