484 FOSSIL TURTLES OF NORTH AMERICA. 
Mexico. The exact locality is Coal Creek Canyon, in the southeastern corner of San Juan 
County. The specimen bears the catalog number 6090. The skull is quite complete, with the 
exception of the absence of the lower jaw. Figures of the object as seen from above, from below 
and from the right side are presented. 
The skull is that of a large and evidently aged individual and no sutures are to be observed. 
The premaxilla and the anterior extremities of the maxilla are missing, but the missing 
parts would add little to the length of the snout. The distance from the front of the nasal bones 
to the extremity of the occipital condyle is 127 mm. The breadth across the zygomatic arches 
is 111 mm.; the distance from the outside of one quadrate to that of the other appears to have 
been about 88 mm.; and the width across the skull at the middle of the tympanic cavities 1s 
108 mm. It will be seen therefore that the roof of the tympanic cavity projects much over the 
pedicels of the quadrates. Usually in living trionychids the breadth across the pedicels of the 
quadrates is as great, or nearly as great, as the breadth at any other part. The hinder portion 
of the skull is shortened. The extremity of the condyle is only 13 mm. behind the line joining 
the quadrates. In a specimen of Platypeltis ferox 94 mm. long from the snout to the condyle, 
the latter is placed at a distance af 17 mm. behind the quadrates. Relatively to other species 
of the group the skull is broad, the breadth being 86 per cent. of the length. In Pelochelys 
cantoris, Whose skull is relatively broad, the width of the latter is 82 per cent. of the length. 
The skull of the species under description is flat, and this appears to be due in no measure 
to crushing. Placed on a level surface, the skull has its crest elevated to a height of 65 mm. 
The snout was blunt. The skull maintains its breadth as far forward as the line joining 
the posterior borders of the orbits, where itis g8 mm.; then the outlines converge rapidly. 
The interorbital space is 15 mm. wide. The orbits look outward, forward, and upward, and 
are circular, with diameters of 22 mm. From the orbits the sides of the face slope downward 
and outward. 
The anterior nasal opening appears to have had little height, rising only 8 mm. above the 
floor of the passage. Its breadth has been 20 mm. The lateral crests of the parietals converge 
rapidly and meet opposite the fronts of the prootics. The postorbital arch has a width of 
11mm; the zygomatic arch a width of only 8 mm. in the middle of its length. At its anterior 
inferior border it starts from the hinder extremity of the cutting-edge of the maxilla,and ascend- 
ing passes backward to the front of the tympanic cavity. It is far more archt than that of 
living trionychids. The tympanic cavity is relatively longer than that of Platypeltis ferox, the 
length being 33 mm., one-fourth the length of the skull. In ferox the length of the cavity is 
about one-fhfth the length of the skull. 
In contradistinction to P. ferox, the upper border of the squamosal is not rolled down- 
ward, but stands out as a sharp edge. Moreover, there does not appear to have existed 
that long backwardly directed process of the squamosal and paroccipital which we find so 
conspicuous in the living trionychids. It is possible that this process was originally somewhat 
longer than now appears; but it could have been but little longer. 
The fossa inclosed by the zygomatic arch is greatly different from that of Platy peltis. 
In the latter, and perhaps in all living members of the Trionychide, the fossa is longer than 
broad. In this Puerco species the length is 34 mm., the width about 38 mm. 
The occipital crest has been injured and is partly missing. It included a lower horizon- 
tally expanded border and a thickened superior border. The latter may be, so far as preserved, 
the backwardly prolonged parietals. 
The upper jaws were furnisht with subacute cutting-edges. From these the palate rises 
in a high vault, 26 mm. above the cutting-edges. The choane are removed far backward, 
their front borders touching a perpendicular plane thru the posterior borders of the orbits. 
The distance from the premaxille to these choanz was about 50 mm. There was, therefore, 
an enormous crushing surface on the upper jaws, and we may conclude with safety that the 
animal was accustomed to devouring a prey that was protected by hard coverings, such as 
mollusks. From each choana a groove in the roof of the mouth extends backward about 30mm. 
The pterygoid region is only 36 mm. wide. In the specimen of Platypeltis ferox referred 
to, the pterygoid region is eight-tenths the width of the upper jaws. This region in the fossil 
is very concave transversely. The articulation of the quadrate was about 20 mm. wide. 
This skull is the most ancient one of the Trionychide that is at present known. 
