TRIONYCHID&. 535 
sixth costal plate nearly complete, fragments of several other costals, nearly the whole of the 
right hyoplastron, the mesial two- thirds of the right hypoplastron, one cervical vertebra, the 
proximal portion of the right femur, the distal ae of the right humerus, and some other, but 
unimportant, fragments. "Whether or not there was a preneural can not yet be determined. 
The individual was a very large one, the plastral bones indicating that the width of the 
plastron was little short of 600 mm. An estimate, not wholly reliable, made from the costals 
present, indicates that the length of the carapace was about 500 mm. It is quite probable that 
the carapace was at least as broad as long. 
The skull was correspondingly long. A comparison of the united quadrate and prootic 
with those of Platypeltis ferox indicates a length of skull of 225 mm. from snout to occipital 
condyle, but little less than nine inches. The fragment of maxilla indicates a shorter skull, 
about 7 7 inches. It is not improbable that the front of the skull was relatively short. “The 
quadrate and prootic offer no peculiarities when compared with those of P. laty peltis ferox, 
except that in the latter the anterior ends of the borders which articulate with the parietal and 
the quadrate respectively rise considerably as they approach these bones, thus making the 
anterior end of the prootic somewhat gutter-like; whereas, in 7. manducans the rise of the 
prootic on each side is slight and the front border of the bone is quite flat. 
The fragment of the maxillary offers the most interesting modification. Fig. 2 of plate 105 
represents the bone from the outside; fig. 3 from below. The lower border of the bone forms 
a prominent cutting-edge, such as we find in many other trionychids. Inside of this cutting- 
edge there is, in other trionychids, a horizontal masticatory surface which may be very narrow 
‘ 
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the 
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Fic. 690.—T emnotrionyx manducans. Plastron of type.  ¢. 
or of moderate width, or very broad; but it is always nearly plane. In 7. manducans, on the 
contrary, this masticatory surface is traverst from one end to the other by a sharp ridge, such 
as we find in various Emydide and Testudinide. ‘The ridge is not at all tootht. Mesiad of it 
the palatal surface of the bone past inward and somewhat upward to the choanz, and to meet 
the vomer in front and the palatine behind. The structure of the jaw indicates that the animal 
was accustomed neither to seizing and swallowing whole a living prey nor to crushing shells 
and other hard objects; but rather to masticating animal and vegetable substances of a mod- 
erate hardness. 
The nuchal bone offers one peculiarity. In the midline, on the under side equally removed 
from the anterior and the posterior borders, is an oval depression 14 mm. long and 10 mm. 
wide. It probably served as the attachment of a ligament. The bone does not come to an edge 
in front, but is truncated. The thickness is 16 mm. The antero-posterior extent of the bone 
was 55 mm. The lateral extent is unknown. There appears to have been a smooth band 
along the anterior border, narrow at the midline, while the remainder is covered with shallow 
pits, 4 or § in a 20 mm. line. 
Some of the costals indicate a considerable convexity of the carapace. One fragment from 
the middle of the length of the shell has a width of 65 mm. and a thickness of 10 mm., near the 
sutural border. The sixth costal is 51 mm. wide proximally and 95 mm. wide at the free border. 
Its thickness is 12 mm. at the posterior sutural border. The upper layer of the bone of the 
costals overhung somewhat the middle layer, so that there was a sharp channel running around 
the border of the carapace. Notwithstanding the age of the individual the ribs projected con- 
siderably beyond the borders of the disk, in one case 42 mm. 
