TRIONYCHIDZ. 491 
The total length in the midline is 538 mm.; the greatest width, 665 mm. The greatest 
height of the center of the carapace above the distal ends of the costals is only about 70 mm., 
but in life the height may have been somewhat greater. The nuchal has an antero-posterior 
extent of 75 mm., and an extent from side to side of 400 mm. There was probably a preneural 
bone, but this region is damaged so that the presence of the bone is uncertain. If it was not 
developt, the first neural must have been very large. Furthermore, there are some appearances 
in the region in question which indicate that there was a preneural. The probable condition 
in this part of the carapace is indicated in the text-figure (fg. 646). In the carapace, as restored, 
there seems to be a suture between the inner anterior angle of the first left costal and a pre- 
neural; but the supposed suture may be merely a fracture. There is also a fragment of bone 
which appears to be a portion of the preneural and a portion of the first Nencal: but it is un- 
certain whether or not the fragment belongs where it is placed. If present, the preneural was 
probably wider at its anterior end than at the posterior. On the other hand, a very large 
—— first neural, like that of Amyda egregra, may 
—— have occupied the entire space between the first 
Sy costals. The evident relationship of this species 
to Aspideretes coalescens Cope, as figured by 
oe ns Lambe under the name Trionyx vagans, renders 
: the presence of the preneural more probable. 
ee, \, Behind the preneural there were 7 neurals. 
; \ ; a = These had the usual coffin-shape, with the nar- 
ie ee | rower ends directed forward, except the sixth, 
po axe which is oval in form, and the seventh, which 
a en : . | has the broader end in front. The neurals 
mostly decrease in size from the first to the last. 
r\ ; The table below gives the dimensions of the pre- 
sab, Se : t neural and the neurals. 
{ | ce The first, seventh, and eighth costals are 
considerably broader at their proximal, than at 
\ ; : their distal, ends; and the first is broadest of 
| — ) all, its width near the neural being 88 mm. 
| : \ pon Distally it is contracted to 52 mm. The next 
ae three costals are about 60 mm. wide near the 
Fic. 646.—Aspideretes splendidus. Carapace of neurals, the second and the fourth about 110 
type. Xd. No. 3952 A. M.N. H. mm. distally, and the third 87 mm. The sixth 
and seventh costals measure about 50 mm. each 
proximally, while distally their widths are respectively 108 mm., 133 mm., and 25 mm. The 
eighth pair meet along the midline for a distance of 46 mm. while they form 230 mm. of the 
hinder border of the carapace. The thickness of a costal at its sutural border and in the 
middle of the length is to mm., while thru the rib the thickness is 14 mm. At their distal ends 
the costals are beveled off to an edge. 
= = —_ The ornamentation consists of abrupt and narrow ridges 
Rigen: Length. Width, | Which by their union inclose pits and furrows of irregular 
size and form. There are usually 3 pits or furrows in a dis- 
tance of 10 mm.; but in places there may be only 2, or again, 
wi heclaae pe _ asmanyas 4. They are largest on the middle of the lengths 
Neural 2 60 46 of the anterior and middle moseals and over nearly the whole 
iele : a A ve surface of the hindermost costals; they are smallest along 
Neursi'e..-o1 a8 re the middle of the back and on the distal ends of the costals 
Neural 6..... 42 2 of the anterior half of the shell. Toward the free borders of 
Neva ae: 33 3 the costals the pits diminish in size, and finally the beveled 
border is left nearly smooth. In some places near the distal 
ends of the costals (plate 88, fig. 8) the pits are nearly quadrate and in rows. 
On plate 88, fig. 7 shows the sculpture on the outer third of the second costal, the upper end 
of the fgure being the more anterior, the right side being toward the middle line of the 
