542 FOSSIL TURTLES OF NORTH AMERICA. 
the midline is 132 mm.; the extreme width is 117 mm. The carapace (fig. 699) is moderately 
convex. The anterior border is broadly rounded; the hinder border is excavated. There 
were originally 6 neural bones, of which the first is injured and the fourth is missing. The first 
had a length of 21 mm. and a width of 10 mm. The others are shorter and narrower. The 
nuchal has a fore-and-aft extent of 18 mm. and a length of 66 mm. from side to side. There 
are only 7 pairs of costals. Those of the seventh pair meet at the midline. The costals are 
about 3 mm. in thickness. The sculpture of the specimen agrees with that of the type, but it 
is more feebly developt. The surfaces of the neurals and the proximal ends of the costals 
present shallow pits arranged irregularly. Of these pits there are from 5 to 7 ina line 10 mm. 
long. Toward the distal ends of the costals the pits become smaller and more closely packt, 
there being about 10 in a 10 mm. line. 
The greater portions of both hyoplastra and both hypoplastra accompany the carapace. 
There was a considerable fontanel between the hypoplastrals in front and the xiphiplastrals 
behind. The mesial half of the hyoplastra and of the hypoplastra are only 3 mm. thick; but 
the thickness is somewhat greater near the distal ends of the bones. The bridges are 26 mm. 
wide. The length of the hyohypoplastral suture is 61 mm. The sculpture of these bones is 
greatly like that of the carapace. 
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Fics. 699 AND 700.—Platy peltis trionychoides. X34. 
699. Carapace of No. 5938 A. M. N. H. 700. Plastron restored from No. 5938 and No. 6017 A. M. N. H. 
The limb bones present show no important differences when compared with those of P. 
spinifera. : 
No. 6017, of the American Museum of Natural History, was found at Grizzly Buttes in 
1903. It furnishes fragments of the costals, some neurals, and nearly the whole of the plastron 
except the entoplastron and the epiplastra, elements of the plastron rarely recovered, on 
account of their loose attachment and their delicate construction. This specimen differs from 
the preceding only in the boldness of the sculpture, the pits being deeper and the ridges higher 
and sharper. It is coarsest on the outer ends of the hyoplastrals and the hypoplastrals.. From 
this specimen has been drawn most of the plastron as represented in fig. 700, but parts of 
this figure have been taken from the plastron of No. 5938. 
No. 5942, American Museum, also from Grizzly Buttes, belonged to a larger and an older 
individual than the specimens already described. The hyoplastron is co-ossihed with the 
hypoplastron. Following the line of the missing suture, the distance is g2 mm. The bones 
are a little over 4 mm. thick on the mesial half; at the bridge they are about 8 mm. thick. 
The sculpture is strongly exprest, especially on the bridges. 
The xiphiplastron differs in having the outer border, near the base of the process entering 
the hypoplastron, expanded outward. This is due probably to the greater age of the animal, 
The bone is 5 mm. thick; that of No. 6017 is 4 mm, 
