24 FOSSIL TURTLES OF NORTH AMERICA. 
originally was, but it is now overlain by the dermal mosaic. Mr. Newman holds also 
that the peripherals and the suprapygals are dermal bones, not what the writer called 
fascia bones or subdermal bones. If the reader will consult the succeeding pages that 
deal with Toxochelys he will see that one of the dermal nodules overlies the second 
suprapygal. ‘The latter is therefore not equivalent to the row of nodules in front 
of it and to those on the tail of the snapping-turtle, but is a bone of a deeper layer. 
We may, therefore, for the present regard the characters of the most primitive 
turtles as having been the following: There was a superficial armor composed of 
dermal bones arranged in at least 7 zones above and at least 5 zones below, with 
many bones in each zone, and each bone covered by a horny scute. Beneath this 
was a subdermal armor. On the upper side of the body, this consisted of the nuchal, 
a row of neurals, 8 pairs of costal plates, suprapygals, and peripherals; below, of 
the entoplastron and at least 5 pairs of subdermal bones. ‘There were 18 presacral 
vertebra, of which 10 belonged to the trunk and were without transverse processes 
and more or less immovyably joined to each other and to the ribs and neural plates. 
The neck was short and consisted of 8 biconcave vertebra, which possest transverse 
processes and low neural spines. ‘There may possibly have been present some 
cervical ribs. ‘There were 2 sacrals. “The tail consisted of biconcave vertebre, 
each provided with free ribs, with chevron bones below, and perhaps with one or 
more rows of bony nodules above. 
The skull had a complete temporal roof, but the temporal fossa was probably 
not widely open behind. There were nasals, lacrimals, and prefrontals, all 
distinct from one another. “There was no parietal foramen. A vomer was present 
but no prevomers. The choanz opened far forward in the roof of the mouth. The 
quadrate was fixt, somewhat excavated to form a tympanic cavity and notcht 
behind for the stapes. Probably the palate was closed by the union of the pterygoids 
with each other and with the basisphenoid. The parietals may or may not have 
sent down each a plate to the pterygoid, in front of the exit of the trigeminal nerve. 
The paroccipitals were free from the exoccipitals. “UVhe jaws were without teeth and 
were covered by a sheath of horn. Each ramus of the lower jaw was doubtless com- 
posed of 7 elements, and the dentaries were probably not co-ossified at symphysis. ‘I he 
outer surface of the bones of the skull was covered by horny scutes. ‘I he shoulder- 
girdle consisted of a pair of coracoids, a pair of scapula, and a pair of procoracoids; 
the latter probably co-ossifying somewhat late in life with the scapula. Limbs, fore 
and hinder, probably not greatly different from those of living Chelydridz, but more 
crudely modeled. “Lhe phalangeal formula was 2, 3, 3, 3, 3 in all the feet. 
If the views exprest above regarding the original composition of the armor of 
turtles is correct, the possession of a carapace consisting exclusively of a mosaic 
of dermal plates, as in Dermochelys, is a secondary character; as 1s likewise the 
possession of a shell constituted only of the deeper elements, as in the great majority 
of turtles. Other secondary characters are the absence of entoplastron (Dermo- 
chelys, Kinosternon), the absence of peripherals (Trionychotdea), and the absence of 
mesoplastra, as in most living turtles. Such too is the lack of nasals and lacri- 
mals in the great majority of turtles. ‘The adaptation of the limbs for habitual 
swimming is, of course, a secondary modification of these organs. 
In this category, too, belong those modifications of the cervical vertebra by 
virtue of which the neck has become so greatly elongated in most forms and made 
most freely flexible in a horizontal plane in the Pleurodira and in a perpendicular 
plane in all the others. Most extraordinary of all the secondary characters is that 
complex of modifications which permits the head and neck to be retracted between 
the scapulz, the loop in the neck sometimes reaching backward quite to the pelvis. 
